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African Crop Science Journal
African Crop Science Society
ISSN: 1021-9730 EISSN: 2072-6589
Vol. 5, Num. 2, 1997, pp. 107-117
African Crop Science Journal
Vol.5. No.2, pp.107-117, 1997

Improved polyploid musa germplasm developed through ploidy manipulations

R. ORTIZ and D. VUYLSTEKE^1

Plantain and Banana Improvement Programme, International Institute of Tropical Agriculture (IITA), High Rainfall Station, Onne, PMB 008, Nchia-Eleme, Rivers State, Nigeria
Current address: The Royal Veterinary and Agricultural University, Department of Agricultural Science, 40 Thorvaldsensvej, DK 1871 Frederiksberg C, Copenhagen, Denmark
^1 IITA-East and Southern Africa Regional Centre, P.O. Box 7878, Kampala, Uganda

(Received 28 January, 1997; accepted 2 June, 1997)


Code Number: CS97017
Sizes of Files:
    Text: 41.9K
    Graphics: Photographs (jpg) - 166.6K  

ABSTRACT

Plantain and banana (Musa spp. L.) polyploid hybrids have been obtained after interspecific hybridisation and ploidy manipulations (i.e., interploidy crosses). The identification of promising hybrids for cultivar release requires their field testing to assess agronomic performance. The potential of new polyploid hybrid selections was evaluated in comparison with their triploid ancestral landraces in two trials consisting of 25 and 30 genotypes, respectively. Twenty-six primary tetraploids, seven secondary triploids, three secondary tetraploids and one tertiary tetraploid hybrid were evaluated along with seven triploid landraces and three diploid ancestors from 1993 to 1996. Following this extensive on-station field testing and fruit taste panels, seven promising hybrids were selected based on their desirable attributes: desired resistance to biotic stresses, acceptable agronomic traits and adequate fruit quality. The selected hybrids were the black sigatoka-resistant and virus- tolerant primary tetraploids TMPx 7152-2 (plantain), TMPx 7356-1 (plantain), TMBx 5295-1 (starchy banana), and the secondary Musa triploids (TM3x) 14604-35, 15108-1, 15108-2, and 15108-6. This improved germplasm has been advanced for multilocational trials in Nigeria and for local testing in Uganda. After assessing their stability and local adaptation, they may be released as new cultivars in specific agroecozones. The final impact of these Musa hybrids in African agriculture will be measured when this new germplasm becomes an integral component of local farming and food systems.

Key Words: Banana, breeding, heterosis, hybrids, plantain, polyploidy

RESUME

L'hybridation et les manipulations ploodiques, c'est-a-dire les croisements interploidiques, ont permis d'obtenir les hybrides polyploides des plantains et des banaiers (Musa spp. L.). L'identification des hybrides prometteurs susceptibles de donner lieu aux cultivars necessite un essai au champ en vue d'evaluer leur performance agricole. Le potentiel de nouveaux hybrides selectionnes a ete evalue en les comparant a leurs races ancestrales triploides. Cette comparaison a ete effectuee dans deux essais composes respectivement de 25 et 30 genotypes. 26 tetraploide primaires, 7 triploides secondaires, 3 tetraploides secondaires et l'hybride tetraploide tertiaire ont ete evalues en meme temps que 7 races terrestres triploides et 3 ancetres diploides de 1993 a 1996. A partir de ce vaste essai en champ et de la liste des preferences des fruits, 7 hybrides prometteurs ont ete selectionnes en fonction des criteres suivants: la resistance souhaitee aux contraintes du milieu, les traits agronomiques acceptables et la qualite adequate des fruits. Les hybrides selectionnes etaient les tetraploides primaires noirs resistants au sigatoka et tolerants aux virus. Il s'agit de tetraploides TMPx 7152-2 (plantain),TMPx 7356-1 (plantain), TMBx 5295-1 (bananier feculent), et de triploides secondaires de Musa (TM3x) 14604-35, 15108-1, 15108-2, et 15108-6. Ce germoplasme ameliore a ete introduit au Nigeria pour des essais multilocalites et en Ouganda pour des essais locaux. A pres l'evaluation de leur stabilite et de leur adaptation au niveau local, on peut les promouvoir comme nouveaux cultivars dans les agroecozones specifiques. L'impact final de ces hybrides de Musa dans l'agriculture africaine sera mesure losque ce germoplasme deviendra une composante integrale de l'agriculture locale et des systemes alimentaires.

Mots Cles: Bananier, reproduction, heterosis, hybrides, plantain, polyploides

INTRODUCTION

Africa is the largest producer of plantains and cooking bananas (Musa spp. L.), followed by tropical America and Asia (FAO, 1993). The crop is grown mainly by African smallholders who produce plantains and bananas in their compound or home gardens (Vuylsteke et al., 1993a). The most important cultivars are almost sterile triploids and are old landraces selected by farmers several hundred years ago (Simmonds, 1995).

Pest pressure has increased in recent years in Africa (Vuylsteke et al., 1993a). Hence, breeding for resistance has been pursued actively to overcome yield losses due to the susceptibility of old landraces, especially to the fungal leaf spot black sigatoka (Mycosphaerella fijiensis Morelet) (Ortiz et al., 1995).

Musa breeders of the Plantain and Banana Improvement Programme (PBIP) of the International Institute of Tropical Agriculture (IITA) are developing improved plantain and banana germplasm with resistance to pests, high and stable yield, and good fruit quality (Vuylsteke et al., 1993b, 1995). New selections are released after testing their performance in at least early and preliminary yield trials (PYTs) in the breeding station. This paper discusses the results from preliminary yield trials carried out in southeastern Nigeria from 1993 to 1996. Primary and secondary polyploids along with their parents were tested in these experiments.

MATERIALS AND METHODS

Two preliminary yield trials (PYT-93 and PYT-94) were planted in IITA's High Rainfall Station at Onne (southeastern Nigeria). Data were collected for the plant crop and successive ratoons of PYT-93 and for the plant crop of PYT-94. Selection of hybrid entries for both PYTs was done in plant and ratoon crops of unreplicated early evaluation trials.

Plant materials. PYT-93. Twenty-five clones (listed in Tables 1 and 2) were assessed in this trial: 17 tetraploid plantain hybrids, 3 tetraploid cooking and starchy banana hybrids, 3 triploid plantain landraces, 1 triploid cooking banana and 1 triploid starchy banana. All hybrids were derived from interploidy crosses between a triploid plantain or banana and a wild or cultivated diploid banana. The trial was planted with in vitro propagules (Vuylsteke, 1989).

Table 1. Preliminary yield trial in sole crop of Musa germplasm at Onne (1993-94)

---------------------------------------------------------------------------
Clone      DF  TNL  PH  NSLf YLSf HTSh  DFF   BW   H  F  FL    FC
          days  #   cm   #    #    cm   days  kg   #  #  cm    cm
---------------------------------------------------------------------------
Tetraploid plantain hybrids

548-4*    295   28   299   11    8   206   105    7.6    6   72   17   12
548-9*    253   25   293   13   11   312   115   11.3    6   84   17   13
582-4     254   25   240   12   10   202   120    8.4    6   82   17   12
1112-1*   268   22   287   10    9   213   118    7.4    7   96   17   11
2637-49*  289   29   304   11   10   200   108    8.9    6   83   19   12
2776-20   260   22   272    9    7   186    82    3.3    5   64   12   10
2796-5*   258   26   306   14   12   210   113   11.8    6   89   19   13
4479-1*   303   26   265   11    8   174   102    8.1    6   76   17   12
4698-1*   314   29   276    9    7   178   118    7.8    8   99   18   11
4744-1    248   26   283   13   12   240   122    8.8    6   72   16   13
5706-1*   284   27   295   10    8   173   111    7.2    7   90   16   12
5860-1    173   24   233   12   11   186   114    4.0    4   45   18   11
6930-1OT  339   25   249    9    6   216    99    4.5    6   69   14   11
7152-2    239   25   278   12   12   243   116    8.0    6   79   20   11
7356-1    260   26   311   11   10   278   111    9.4    6   80   19   12
10091-2   311   25   240    9    6   188   100    6.2    6   77   18   12

Triploid plantain landraces (check cultivars)

Agbagba   262   29   300   10    6   160    95    5.9    5   20   26   15
B. Tannap 346   28   272    6    4   142    82    4.2    6   63   15   11
O.l'Ewai  303   29   311    9    7   113    98    9.1    7   75   20   13

Tetraploid banana hybrids

612-74    237   23   282   15   14   260   146   10.3    6   67   18   14
5295-1    363   27   314    8    7   110    89   11.0    7   84   24   13
5748-1    346   30   277    8    5   170    98    3.7    6   71   15   10

Triploid bananas   

Cardaba   353   23   269    8    5   138    99    4.7    5   56   14   12
Pisang    
Kelat     310   26   268   12   10   202   129    4.5    6   78   13   10

P(F-test)    <0.001      <0.001     0.007       <0.001     <0.001    <0.001
         0.004      0.001     <0.001      0.011        <0.001   <0.001 
CV (%)     14   11    7    20   24    14    26     26   10   15   11   10
DF = days to flowering; TNL = total number of leaves; PH = plant height; NSLf= number of standing leaves at flowering; YLSf = youngest leaf spotted at flowering; HTSh = height of tallest sucker at harvest; DFF = days to fruit filling; BW = bunch weight plant-1; H = number of hands; F = number of fruits; FL = fruit length; FC = fruit circumference, CV = coefficient of variation, OT = offtype.
* registered hybrid (Vuylsteke et al., 1993a, 1995)
---------------------------------------------------------------------------

Table 2. Preliminary yield trial in sole crop of Musa germplasm at Onne (ratoon1994-96). Most of the bunch weight and its components were recorded on virus-symptomless plants

---------------------------------------------------------------------------

Clone        DF  TNL   PH   NSLf YLSf HTSh   DFF    BW    H    F   FL    FC
            days  #    cm    #    #    cm   days    kg    #    #   cm    cm
---------------------------------------------------------------------------
Tetraploid plantain hybrids
 
548-4*       -z   23   287   11    9   268   128    9.0   5    81   18   13
548-9*       95   26   326   11   10   269   119   17.4   6   104   18   14
582-4*       92   26   291   11    8   219   120   11.2   6    88   18   13
2637-49*    156   28   333   11    9   274   121    9.6   6    84   18   12
2796-5*      -z   27   350   13   11   280   112   20.0   6   107   20   14
4479-1*     185   26   321   11   10   245   122   13.4   6    94   21   14
4744-1      144   26   334   12    9   269   117    8.8   6    83   16   13
5706-1      154   26   318    8    6   265   103    4.6   6    76   14   10
6930-1 OT   106   23   274   10    7   211   129    4.1   6    81   12    9
7152-2       96   28   332   12   10   270   118   12.4   7    99   22   12
7356-1      173   26   363   12    9   248   115   12.6   7    99   20   13
10091-2     135   23   266    8    6   206    98    5.8   5    65   13   10
 
Triploid plantain landraces (check cultivars)   
 
Agbagba     177   23   325    9    5   178    84    5.3   6    19   24   15
B. Tannap   205   25   292    8    6   160    94    8.0   6    78   17   12
O.l'Ewai     -z   26   328    9    7   161    97    8.6   7    71   19   13
 
Tetraploid banana hybrids
 
612-74       99   26   344   13   10   253   132   14.2   6    82   18   15
5295-1      299   28   336   11    9   142    88   15.4   8    98   25   13
5748-1      175   28   335   11    9   282   115    6.8   7    81   17   11
 
Triploid bananas   
 
Cardaba     212   23   299   10    8   199   121   8.8   6   65   15   14
Pisang Kelat146   26   269   12   10   190   130   4.2   6   78   11    9
 
P(F-test) <0.001     <0.001     <0.001     <0.001     <0.001    <0.001   
                0.060      <0.001     0.046      <0.001    <0.001    <0.001
CV (%)      38    11    7    14   20    26    11    23  12   18   11   10
 
DF = days to flowering; TNL = total number of leaves; PH = plant height; NSLf= number of standing leaves at flowering; YLSf = youngest leaf spotted at flowering; HTSh = height of tallest sucker at harvest; DFF = days to fruit filling; BW = bunch weight plant-1; H = number of hands; F = number of fruits; FL = fruit length; FC = fruit circumference, CV = coefficient of variation, * registered hybrid (Vuylsteke et al. 1993b), - = missing data; OT = offtype
z Mother plants were destroyed before flowering by strong wind damage in the ratoons. Therefore, calculation of DF may be biased towards high values. The other data were collected on the best follower which became the mother plant on the respective ratoon cycle
---------------------------------------------------------------------------

PYT-94. Thirty clones (listed in Table 3) were assessed in this trial: seven secondary triploid plantain-derived hybrids, three secondary tetraploid plantain-derived hybrids, seven primary tetraploid plantain hybrids (mostly parents of secondary polyploid hybrids), four primary tetraploid cooking banana hybrids, one tertiary tetraploid cooking banana hybrid, two triploid plantain landraces (grandmothers of secondary polyploid hybrids), three cooking banana landraces (ancestors of cooking banana hybrids), one selected diploid hybrid (parent of some secondary triploid hybrids), one plantain-derived diploid (parent of some secondary triploids), and one wild banana (grandparent of all secondary polyploid hybrids). Secondary triploids were obtained from tetraploid-diploid crosses between primary tetraploid plantain hybrids and selected diploid banana or plantain-derived parents. Secondary tetraploids were selected after intermating primary tetraploid hybrids. This trial was also planted with in vitro propagules.

Table 3. Preliminary yield trial in sole crop of Musa cultivars at Onne (plant crop, 1994- 1996)

---------------------------------------------------------------------------
Clone        DF   TNL  PH  NSLf  YLSf  HTSh  DFF    BW    H    F   FL   FC
            days   #   cm   #     #    cm   days    kg    #    #   cm   cm
---------------------------------------------------------------------------
Secondary plantain-derived triploids
 
14123-5     340   24   256   11    8   151   103    9.0    5   65   19   13
14123-6     546z  21   213    8    6   160    91    BSV   
14604-35    302   28   275   14   13   209   125   14.0    7  112   21   13
14604-37    250   30   229   13   10   254   117    6.4    7   92   17   10
15108-1     333   21   215   12    9    64   116   11.6    8  119   16   11
15108-2     321   27   268   14   12    47   102   12.7    7  106   22   12
15108-6     329   27   239   9     7   223   133   14.4    7  127   18   13
 
Secondary plantain-derived tetraploids
 
15090-102   241   25   229   12   10   281   153    9.1    6  112   18   13
15090-130   290   25   201   13   12   215   163    6.8    7  112   14   11
15955-3     313   25   265    9    7   293    97    6.9    8  110   17   11
 
Primary tetraploid parents of secondary plantain-derived triploids
 
548-4*      BSV + WD
582-4*      274   25   211   11    9   236   119    7.2    5   69   16   12
1187-8(BSS) 387   21   179    9    7   158   117    2.2    6   65   12   10
4479-1*     321   24   276   11    9   229   111    9.0    6   74   20   13
4698-1*     364   29   276   11    9   224   108    9.5    7   95   18   12
6930-1*     339   28   238   12    8   151   124    8.9    7   84   17   12
15063-1     343   23   265   11    8   136   112    8.1    6   69   20   13
 
Selected diploid parents of secondary plantain-derived triploids
 
1549-7      204   26   186   13    8   234   109    1.2    7   85    7   4
SH-3362     529   29   240    9    7   226   114    7.8   11  141   14   9
 
Grandparental triploid plantain landraces
 
B. Tannap   353   26   298    8    6    74    89    7.2    6   65   21  13
O. l' Ewai  396   24   290    8    5    70    72z   3.2z   5z  59z  17z 11z
 
Grandparental diploid wild banana 
 
Calcutta 4  208   22   174   12    -   247   126    0.5    6   81    6   4
 
Parental triploid cooking banana landraces
 
Bluggoe     345   27   311   10    7   256   126   10.8    5   52   19  16
Cardaba     313   28   300   11    9   269   136   13.6    6   77   17  15
Fougamou    376   32   303   12    8   308   116   5.8y    9  135   10z  9z
 
Cooking banana primary tetraploids
 
612-74 OT:
CAM         266   24   260   15   13   265   156   9.7     6   64   17  14
KUL         287   23   251   14   11   237   152   9.4     6   58   17  14
Onne        319   25   206   13   11   174   160   6.6     5   45   17  14
1378        399   29   311   12    9   206   118   4.1y    8  113    9z  9z
 
Cooking banana tertiary tetraploid
 
FHIA-3      318   26   266   11    9    80   102  16.9     8   125  17  14

P(F-test) <0.001     <0.001     <0.001     <0.001       <0.001    <0.001   
                <0.001     <0.001     <0.001     <0.001      <0.001  <0.001
CV (%)       10   12    8    13   19    18    11    23    11    17  11  10
 
DF=days to flowering, TNL=total number of leaves, PH=plant height, NSLf=number of standing leaves at flowering, YLSf=youngest leaf spotted at flowering, HTSh = height of tallest sucker at harvest, DFF = days for fruit filling, BW = bunch weight plant-1, H = hands bunch-1, F = fruits bunch-1, FL=fruit length, FC=fruit girth, CV= coefficient of variation, BSV=plants were rogued due to BSV, BSS=black sigatoka (BS) susceptible, WD=strong wind broke pseudostem bearing inflorescences and/or bunch, *registered BS resistant hybrid (Vuylsteke et al. 1993b), OT=offtype, -=no leaf spots
z Late flowering because original mother plants were rogued due to strong BSV infection
y Fruits affected by unknown pest during fruit filling
---------------------------------------------------------------------------

Site characterisation and crop management. Onne (4 degrees 43'N, 7 degrees 1'E), a humid forest site, is located in the secondary centre of plantain diversification. Annual rainfall is monomodal in distribution and commonly greater than 2400 mm. The soils are ultisols derived from coastal sediments of the Niger Delta region. They have low pH (<4.3) and low cation exchange capacity. The fields were left to fallow with Pueraria phaseoloides L. for at least two years before planting the PYTs, and prepared with minimum disturbance by manual clearing.

Plants were fertilised at an annual rate of 300 kg N ha^-1 and 450 kg K ha^-1 split over six applications during the rainy season and using urea and muriate of potash, respectively. In addition, approximately 10 kg of mulch from elephant grass (Pennisetum purpureum L.) and 10 kg of pig manure were applied once to each plant in the ratoon. Plants were treated with an insecticide-nematicide (2 g a.i. isofenphos in 1.5 l water per plant, about every 4 months) to control banana weevil and nematodes. No artificial inoculation was required to assess black sigatoka since the causal pathogen is ubiquitous at Onne (Ortiz and Vuylsteke, 1994a).

Field layout and data recording. Experimental designs and plot sizes were those recommended by Ortiz and Vuylsteke (1995) for preliminary on-station yield trials. The PYT-93 was planted in a simple square lattice design with 2 replications of 5 plants while the PYT-94 was a simple rectangular lattice design with 2 replications of 4 plants. Distances between rows were 3m and distances between plants within rows were 2m, giving a plant density of 1667 ha^-1.

Data were recorded on individual plants, i.e., one plant was considered as the basic experimental unit. Bunches were harvested only from virus symptomless plants when green fruits from the oldest hands started yellowing. The characters evaluated were:

    - plant height at flowering (cm), measured to the nearest 1 cm from soil surface to the "V" point, i.e., where the petioles of the two youngest fully opened leaves meet each other;

    - days to flowering, which are the number of days from planting to shooting (i.e., inflorescence emergence) in the plant crop, and from harvest to shooting in the successive ratoons;

    - total number of leaves produced by the plant throughout its growth cycle;

    - number of standing leaves at flowering, counted from the youngest (i.e., the highest) unrolled leaf downwards;

    - youngest leaf spotted by black sigatoka, recorded as the first leaf showing a necrotic dry centre;

    - height of tallest sucker (cm), measured to the nearest 1 cm from soil surface to the "V" point;

    - days for fruit filling or the number of days from shooting to harvest;

    - bunch weight (kg) to the nearest 0.1 kg;

    - number of hands or nodal clusters of fruits per bunch;

    - number of fruits per bunch;

    - fruit length (cm) of a representative sample from the second hand to the nearest 1 cm; and

    - fruit girth (cm) of a representative sample from the second hand.

RESULTS AND DISCUSSION

All plants from the primary tetraploid hybrid 4424-4 and some from other selected primary tetraploid hybrids, except TMPx 4479-1, TMPx 7152-2, TMPx 7356-1, TMBx 612-74 and TMBx 5295-1, showed virus symptoms and were eliminated prior to flowering in the plant crop PYT-93. Also, all plants of the primary tetraploid hybrids 2776-20, 5860-1, TMPx 1112-1 and TMPx 4698-1 were rogued in the ratoon crop of PYT-93 due to their high susceptibility to Musa viruses. Plants of TMPx 6930-1 were not true-to-type, exhibiting an abnormally poor bunch phenotype in the PYT-93. This abnormal phenotype could have been caused by somaclonal variation arising from in vitro multiplication (Vuylsteke et al. 1991).

All plants of the secondary triploid 14123-6 and some plants of TMPx 548-4 were rogued in the PYT-94 because they showed virus symptoms. Also strong winds damaged flowering mother plants of 'Obino l'Ewai' twice during the fruit filling time, and those of TMPx 548-4 before shooting in the plant crop of PYT-94. The fruits of the primary tetraploid cooking banana TMBx 1378, as well as those of its triploid landrace parent 'Fougamou', were infected by an unknown pest during the fruit filling time in the PYT-94. All offtypes of TMBx 612-74, obtained after in vitro propagation, showed abnormal phenotypes with poor horticultural performance in the PYT-94.

Because of the virus susceptibility of some hybrids and the generation of offtypes after micropropagation, results are discussed below among groups. Specific comparisons are only made for those promising hybrids which did not show virus susceptibility and whose phenotype resembles the original true-to-type.

Analysis of variation for growth and bunch characters in PYTs. There were significant differences (P<0.01) among all clones for flowering, plant stature, and sucker growth in both PYTs (Tables 1, 2 and 3). Clones showed significant (P < 0.01) variation for total number of leaves in the plant crop of both PYTs but not in the ratoons of PYT-93. The selected primary tetraploid plantain hybrids (TMPx) showed better ratooning, as judged by the height of the tallest sucker, than their plantain parental landraces. This is due to the hybrids' regulated suckering behaviour controlled by the gene Ad (Ortiz and Vuylsteke, 1994b). The fast growth of TMPx may explain why they had a shorter flowering time than their landraces in the successive ratoons.

Days to flowering showed a high coefficient of variation in the ratoon of PYT-93 because there were follower plants, especially in the hybrids, which sometimes flowered even before the mother plant was harvested. The black sigatoka resistant TMPx exhibited a longer fruit filling time than their plantain landraces, yet the growth cycle of the latter was longer because of their late flowering. SH-3362, an improved diploid banana from Fundacion Hondurena de Investigacion Agricola (Rowe and Rosales, 1993), flowered late in PYT-94 (Table 3).

The hybrids showed a significant (P< 0.001) variation in their response to black sigatoka (Tables 1, 2 and 3). The previously selected polyploid hybrids exhibited their partial black sigatoka resistant response in both PYTs. The highest levels of black sigatoka resistance were observed in TMBx 612-74 and its somaclonal variants (612-74 CAM, 612-74 KUL, 612-74 ONNE). In contrast, the parental plantain landraces were susceptible to black sigatoka.

Significant differences (P<0.001) were observed among the clones for bunch weight, fruit filling time, number of hands, number of fruits, and fruit size (Tables 1, 2 and 3). In general, black sigatoka resistant genotypes outyielded susceptible clones. The heaviest bunches were harvested from healthy plants of TMPx 548-9 and TMPx 2796-5 in the PYT-93. However, many plants of both hybrids were rogued throughout the experiment because they showed virus symptoms. FHIA-3 had the highest yielding bunches in PYT-94, but the taste of its unripe or ripe cooked fruit was not accepted by the Nigerian panelists (data not shown). Although somaclonal variation did not affect the high resistance to black sigatoka of TMBx 612-74, its somaclonal variants had low bunch weights. This suggests that somaclonal variants are of limited use for the improvement of yield in this cooking banana, as is the case in plantains (Vuylsteke et al., 1996).

The results also showed that high yields are not necessarily associated with the ploidy level. Some secondary triploids significantly (P<0.001) outyielded triploid landraces in PYT-94 (Table 3), while bunches of some black sigatoka susceptible tetraploid hybrids did not exceed the weight of the susceptible triploid landraces. Furthermore, the late flowering SH-3362 had a very high bunch weight for a diploid in the PYT-94. This was not surprising since this selected diploid hybrid was developed after three cycles of phenotypic recurrent selection (PRS) (for a review of its pedigree see Ortiz et al., 1995). This PRS scheme made genetic gains through the elimination of deleterious recessive alleles and the accumulation of favourable additive alleles (Ortiz and Vuylsteke, 1994c). However, the bunch of SH-3362 had many small fruits in PYT-94 (Table 3). This result indicated that the increment in the bunch weight of SH-3362 was based on the production of more fruits but at the expense of individual fruit size.

The breeding value of potential parents for interploidy crosses cannot be established through their phenotype per se since non-additive gene action seems to be very important to achieve heterosis for high yield in Musa (Ortiz,1995). This was corroborated by the poor yields of TMP2x 1549-7, a plantain-derived diploid which was the male parent of the high yielding secondary triploid 14604-35. Non-additive gene action (i.e., intra- and inter-locus interaction) to maximise yields have been reported in other vegetatively propagated polyploid crops (for a review see Peloquin and Ortiz, 1992).

New germplasm releases. Based on the results from these PYTs, seven polyploid hybrids, discussed below, have been selected by IITA for further testing and potential cultivar releases in Africa and elsewhere (Table 4). These selected hybrids should be assessed in multilocational trials in the targeted ecozones, because genotype-by-environment interaction significantly influences their agronomic performance (De Cauwer et al., 1995). They have been sent to recognised virus-indexing centres in accordance with the technical guidelines for the safe movement of Musa germplasm (Diekmann and Putter, 1996) before their international distribution.

Table 4. Hybrids in the process of release

--------------------------------------------------------------------------- 
Genotype     IITA No. Selected in  Attributes          Release  after
--------------------------------------------------------------------------- 
TMBx 5295-1*  BITA-3   1992        BSLS, big fruits, Preliminary on-station 
                                     VT                yield trial 
TMPx 7152-2*  PITA-14  1992        BSR, VT           Preliminary on-station 
                                                       yield trial 
TMPx 7356-1   PITA-18  1992        BSR, VT           Preliminary on-station 
                                                       yield trial 
TM3x 14604-35 PITA-20  1993-1994   BSR               Preliminary on-station 
                                                       yield trial 
TM3x 15108-1  PITA-19  1993-1994   BSR, FWR?, NR?,   Preliminary on-station 
                                     VT                yield trial 
TM3x 15108-2  PITA-15  1993-1994   BSR, FWR?, NR?    Preliminary on-station 
                                                       yield trial 
TM3x 15108-6  PITA-16  1993-1994   BSR, FWR?, NR?,   Preliminary on-station 
                                     VT                yield trial 
* Virus tested stock available from the Transit Centre of the International Network for the Improvement of Banana Plantain of the International Plant Genetic Resources Institute
BSR: partially resistant to black sigatoka; BSHR: highly resistant to black sigatoka; BSLS: less susceptible to black sigatoka, BWR: banana weevil resistant, FWR?: potential for fusarium wilt resistant, MET: multilocational evaluation trial; NR?: potential for nematode resistance; VT: field tolerant to virus (no virus-like symptoms after several years in field surrounded by susceptible plants showing virus symptoms); IITA: International Institute of Tropical Agriculture
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PITA-14 and PITA-18: Short cycling black sigatoka resistant plantain hybrids with field tolerance to virus(es). TMPx 7152-2 (hereafter PITA-14) and TMPx 7356-1 (PITA-18) are black sigatoka-resistant primary tetraploid hybrids derived from the female-fertile French plantains 'Mbi Egome-1' and 'Obino l' Ewai', respectively. The male parent of both hybrids was 'Calcutta 4'. In addition to their black sigatoka resistance, both hybrids had a significantly (P< 0.05) shorter growth cycle than the female landrace parent (Tables 1 and 2) and field tolerance to virus(es) after several years of testing at Onne station. PITA-18 (Fig. 1) is the only hybrid offspring derived from Obino l'Ewai with field tolerance to virus(es) at Onne.

    Figure 1 - PITA-18 (or TMPx 7356-1), a black sigatoka partially resistant tetraploid hybrid (centre), obtained by crossing the susceptible triploid plantain landrace 'Obino l'Ewai' (left) with the highly resistant wild non-edible diploid banana 'Calcutta-4' (right)

This result confirms the complex epistatic nature of virus symptom expression in Musa (Ortiz, 1996). Furthermore, it also suggests that it could be possible to select virus-tolerant black sigatoka-resistant tetraploid hybrids by increasing the population size in the tetraploid hybrid offspring derived from triploid-diploid crosses between plantain landraces and wild bananas.

In the plant crop, both hybrids had similar (P>0.05) bunch weight to Obino l'Ewai (Table 1), but they significantly (P< 0.05) outyielded this plantain landrace in the ratoon at Onne (Table 2). PITA-14 has a lax bunch with long fruit. Both female-fertile hybrids have pendulous bunches with deciduous hermaphrodite flowers and imbricated male bud, and regulated suckering behaviour. In 1995, PITA-18 was rated as the best plantain hybrid by Nigerian taste panelists for unripe boiled and fried ripe fruits (data not shown). PITA-14 was advanced in 1995 for testing in multilocational trials at IITA stations in Nigeria (Abuja, Ibadan and Onne) and for local testing in Uganda.

BITA-3: Black sigatoka and virus tolerant starchy banana. TMBx 5295-1 (BITA-3) is a tetraploid banana hybrid showing tolerance to black sigatoka. Also, this hybrid has not shown virus-like symptoms in early or preliminary yield trials at Onne.

BITA-3 is a hybrid from the cross 'Laknau' (AAB starchy banana) X 'Tjau Lagada' (AA banana). This hybrid significantly (P< 0.05) outyielded the plantain landraces at Onne (Tables 1 and 2). Taste panels showed that fried ripe fruit of BITA-3 was preferred by 38% of the panelists when compared with that of the False Horn plantain 'Agbaga' in a Nigerian dish called Dodo, and by 40% of the panelists when compared with the fruit of the registered hybrid TMPx 2796-5.

This hybrid (BITA-3) is female-fertile, has a pendulous lax bunch with long fruit pedicels, deciduous neutral flowers and imbricated male bud. It exhibits slow sucker development (Tables 1 and 2). BITA-3 has been advanced for multilocational trials in Nigerian humid lowlands, forest-transition zone and Southern Guinea savanna. It has also been sent to Uganda for local testing in the East African mid-altitudes.

TM3x: Secondary triploid plantain hybrids with black sigatoka resistance. TM3x 15108-1 (hereafter PITA-19), TM3x 15108-2 (or PITA-15) and TM3x 15108-6 (or PITA-16) are black sigatoka-resistant secondary triploid hybrids derived from the cross TMPx 4479-1 X SH-3362 (Ortiz and Vuylsteke, 1994d). TMPx 4479-1 is a selected primary tetraploid hybrid developed by crossing 'Bobby Tannap' and 'Calcutta 4' (Vuylsteke et al., 1993). PITA-16 shows tolerance to virus(es) at Onne. The diploid parent of PITA- 16 has shown resistance to fusarium wilt, and its paternal grandparent, SH-3142, is an improved nematode resistant diploid. SH-3142 was developed by FHIA from the highly nematode resistant diploid banana 'Pisang jari buaya' (Rowe and Rosales, 1993). Hence, PITA-16 and its full-sibs may have resistance to fusarium wilt and nematodes, but this remains to be tested.

TM3x 14604-35 (or PITA-20), also a black sigatoka resistant secondary triploid hybrid, was obtained from crossing the selected full-sibs TMPx 6930-1 (tetraploid) and TMP2x 1549-7 (Ortiz and Vuylsteke, 1994d). Both primary euploid hybrids were derived from 'Obino l' Ewai' X 'Calcutta 4' and are partially resistant to black sigatoka (Vuylsteke et al., 1993b; Vuylsteke and Ortiz, 1995).

These selected secondary triploid hybrids (Fig. 2) significantly outyielded (P< 0.05) their parents and grandparents in the plant crop at Onne. Sometimes PITA-16 and PITA-19 exhibited shorter (P <0.05) fruit size than the French plantain landraces (Table 3).

    Figure 2 - TM3x, black sigatoka-resistant secondary triploid hybrids (bottom center), obtained from crossing a black sigatoka- resistant tetraploid hybrid (bottom, left) and an improved diploid banana from FHIA (bottom, right). The tetraploid parent was developed at IITA by crossing the susceptible plantain (top, left) with a high resistant wild non-edible diploid banana (top, right).

The best fruit quality for unripe boiled preparation among the secondary triploids tested in Nigerian taste panels was recorded on PITA-15 (data not shown). Seventeen percent of the panelists preferred the unripe boiled fruits of this hybrid to those of the popular False Horn plantain 'Agbagba'. Also, a similar percentage of panelists favoured the unripe boiled fruits of PITA-15 to those of the registered TMPx 4479-1 (PITA 17). On average, the panelists found that unriped boiled fruits of PITA-15 had acceptable quality. However, when the fruits of this hybrid were compared to those of PITA-16 for "dodo" (fried ripe fruit), 63% of the panelist favoured the latter. This example highlights the problems of breeding a crop with multiple end-uses. Hence, Musa breeders should consider the implications of genotype-by-end use interaction in the development of their improved germplasm. Other preliminary results from taste panels showed that, among the secondary triploids, the most preferred fruit for "dodo" was that harvested from 14604-2. This hybrid is another secondary triploid derived from crosses between TMPx 6930-1 X TMP2x 1549-7 (data not shown). This result may be explained by the fact that secondary triploids obtained by crossing euploid plantain derived hybrids (e.g. PITA-20) may have more plantain alleles than those derived from the cross 15108, which inherited at least 1/3 of their alleles from the diploid banana parent SH-3362.

PITA-16, the highest yielding secondary triploid, has a pendulous dense bunch with curved angular bottlenecked fruits, few persistent neutral flowers and imbricated male bud. This male-sterile triploid hybrid exhibited regulated suckering behaviour (Table 3). PITA-20, also a male-sterile triploid, produces a pendulous dense bunch with persistent neutral flowers. PITA-16 has been advanced for multilocational trials in Nigeria and together with PITA-15 and PITA-19 are being evaluated in Uganda.

REFERENCES

De Cauwer, I., Ortiz, R. and Vuylsteke, D. 1995. Genotype-by-environment interaction and phenotypic stability of Musa germplasm in West and Central Africa. African Crop Science Journal 3:355-362.

Diekmann, M. and Putter, C.A.J. (Ed.), 1996. Musa spp. FAO/IPGRI Technical Guidelines for the Safe Movement of Germplasm 15. FAO/IPGRI, Rome, Italy.

FAO. 1993. Production and Trade Yearbooks for 1992. Vol 46. United Nations Food and Agriculture Organization, Rome, Italy.

Ortiz, R. 1995. Musa genetics. In: Bananas and Plantains. Gowen, S. (Ed.), pp. 84-109. Chapman & Hall, UK.

Ortiz, R. 1996. The potential of AMMI analysis for field assessment of Musa genotypes to virus infection. HortScience 31:829-832.

Ortiz, R., Ferris, R.S.B. and Vuylsteke, D. 1995. Banana and plantain breeding. In: Bananas and Plantains. Gowen, S (Ed.), pp. 110-146. Chapman & Hall, UK.

Ortiz, R. and Vuylsteke, D. 1994a. Inheritance of black sigatoka disease resistance in plantain-banana (Musa spp.) hybrids. Theoretical and Applied Genetics 89:146-152.

Ortiz, R. and Vuylsteke, D. 1994b. Genetic analysis of apical dominance and improvement of suckering behaviour in plantain. Journal of the American Society for Horticultural Science 119:1050-1053.

Ortiz, R. and Vuylsteke, D. 1994c. Inheritance of albinism in banana and plantain (Musa spp.). HortScience 29:903-905.

Ortiz, R. and Vuylsteke, D. 1994d. Preliminary evaluation of secondary Musa polyploids at IITA breeding station. Musafrica (IITA) 5:8-9.

Ortiz, R. and Vuylsteke, D. 1995. Recommended experimental designs for selection of plantain hybrids. InfoMusa 4:11-12.

Peloquin, S.J. and Ortiz, R. 1992. Techniques for introgressing unadapted germplasm to breeding populations. In: Plant Breeding in the 1990s. Stalker, H.T. and Murphy, J.P. (Eds.), pp. 485-507. CAB International, UK.

Rowe, R. and Rosales, F. 1993. Diploid breeding at FHIA and the development of Goldfinger. InfoMusa 2:9-11.

Simmonds, NW. 1995. Bananas Musa (Musaceae). In: Evolution of Crop Plants. Smartt, J. and Simmonds, N.W. (Eds.), pp. 370-375. Longman, London.

Vuylsteke, D. 1989. Shoot-tip culture for the propagation, conservation and exchange of Musa germplasm. Practical Manuals for Handling Crop Germplasm in vitro 2. International Board for Plant Genetic Resources (IBPGR), Rome, Italy.

Vuylsteke, D. and Ortiz, R. 1995. Plantain-derived diploid hybrids (TMP2x) with black sigatoka resistance. HortScience 30:147-149.

Vuylsteke, D., Ortiz, R. and Ferris, S. 1993a. Genetic and agronomic improvement for sustainable production of plantain and banana in sub-Saharan Africa. African Crop Science Journal 1:1-8.

Vuylsteke, D., Ortiz, R., Ferris, R.S.B. and Swennen, R. 1995. PITA-9: A black sigatoka resistant hybrid from the 'False Horn' plantain gene pool. HortScience 30:395-397.

Vuylsteke, D., Swennen, R. and De Langhe, E. 1991. Somaclonal variation in plantains (Musa spp. AAB group) derived from shoot-tip culture. Fruits 46:429-439.

Vuylsteke, D., Swennen, R. and De Langhe, E. 1996. Field performance of somaclonal variants of plantains (Musa spp., AAB group). Journal of the American Society for Horticultural Science 121:42-46.

Vuylsteke, D., Swennen, R. and Ortiz, R. 1993b. Registration of 14 improved Tropical Musa plantain hybrids with black sigatoka resistance. HortScience 28:957-959.

Copyright 1997 The African Crop Science Society


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