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African Crop Science Journal
African Crop Science Society
ISSN: 1021-9730 EISSN: 2072-6589
Vol. 9, Num. 1, 2001, pp. 257-266
African Crop Science Journal

African Crop Science Journal, Vol. 9. No. 1, March 2001, pp. 257-266

The Effect of Crop Rotation on Bacterial Wilt Incidence and Potato Tuber Yield

Berga Lemaga, R. Kanzikwera1, R. Kakuhenzire1, J. J. Hakiza1 and G. Maniz2
PRAPACE, P.O. Box 22274, Kampala, Uganda
1NARO, Kalyengyere Research Station, P.O. Box 722, Kabale, Uganda
2African Highlands Initiative, P.O. Box 239, Kabale, Uganda

Code Number: CS01056

ABSTRACT

To determine the effects of crop rotation on potato bacterial wilt incidence and tuber yields, one-and two-season rotation experiments were conducted during 1995-1999 at Kachwekano Agricultural Research and Development Centre located at an altitude of 2200 meters in southwestern Uganda. Pulses, cereals, root crops and vegetables commonly grown in the area were included in different sets of rotation experiments. Each time, prior to planting the experiment, the field was planted to a bacterial wilt susceptible potato variety and artificial inoculation was also done, when needed, to achieve a somewhat uniform distribution of Ralstonia solanacearum. A one-season rotation in heavily infested field (>90% wilt incidence) with wheat and maize did not significantly reduce wilt but increased ware tuber yield, while the effects of phaseolus beans were not significant. On the contrary, a one-season rotation in mildly infested field (about 15-20% infestation) resulted in a significant reduction in wilt incidence as compared to the control. The highest wilt incidence under rotation was below 13% as compared to 62% in the control. Finger millet and sweetpotatoes reduced wilt the most, while carrots and onions reduced the least. There were no significant yield differences among the rotation treatments except for the control. A two-season rotation on heavily infested soil reduced wilt to 22% - 49% as compared to 81% in the control. The highest wilt reduction was obtained with potato-beans-maize-potato treatment, while the lowest reduction was with potato-maize-maize-potato. Total yields and ware potatoes increased from 3.2 t ha-1 with the control monocrop to 9.3 - 11 t ha-1 with rotation and marketable yields increased from 1.8 t ha-1 to 6.7 - 9.2 t ha-1. Planting different crops in two consecutive seasons performed better than planting the same crop. Interestingly, sweetpotato, which is a major staple food in the area this experiment was conducted, was found to be a good rotation crop for reducing wilt. Beans, the most important food crop and a protein source, but probably a symptom less carrier of Ralstonia solanacearum can be a good rotation crop if used before or after cereals in a potato rotation scheme.

Key Words: Crop rotation, infestations, marketable yield, Solanum tuberosum, ware potatoes, wilt incidence

RÉSUMÉ

Pour déterminer des effets de rotation des cultures sur l'incidence de la bactériose et le rendement des tubercules, des essais d'une saison et de deux saisons ont été conduits en 1995-1999 au centre de développement et de recherche agricole de Kachwekamo, situé à une altitude 2200 m au Sud-Ouest de l'Uganda. Des légumineuses à gousses, des céréales, des plantes à racines et tubercules, et des légumes communément cultivées dans cette région ont été inclues dans des differentes séries d'essais de rotation. Chaque fois, avant l' établissement de l'essai, le champ était planté d'une variété de pomme de terre sensible à la bactériose et une inoculation artificielle était faite, une fois jugée nécessaire pour avoir une uniformité de la distribution de Ralstonia solanacerum. Une saison de rotation dans un champ fortememnt infesté (>90% d' incidence) avec le blé et le maïs n'a pas réduit significativement le mildiou mais a augmenté le rendement des tubercules, alors que les effets des haricots phaseolés n'ont pas été importants. Au contraire, une saison de rotation dans un champ moyennement infesté (environ 15-20% d'infestation) a conduit à une réduction significative de l'incidence du mildiou par rapport au témoin. L'incidence la plus élevée sous rotation était inferieur à 18% par rapport à 62% du témoin. L' eleusine et les patates douces ont réduit le plus le mildiou, alors que les carrotttes et les oignons ont réduit le moins le mildiou. Ils n'y avaient pas de differences significatives entre les traitements de rotation excepté le témoin. Une rotation de deux saisons sur un sol fortement infesté a réduit le mildiou de 22-49% par rapport à 81% pour le contrôle. La réduction la plus élevée du mildiou a été obtenue avec le traitement pomme de terre-haricots-maïs- pomme de terre, alors que la plus faible réduction a été obtenue avec la pomme de terre-maïs-maïs-pomme de terre. Les rendements en tubercules a augmenté de 3.2 t ha-1 chez le témoin monoculture à 9.3-11t ha-1 avec rotation et le rendement commercialisable a augmenté de 1.8 t ha-1 jusqu'a 6.7-9.2t ha-1. La plantation de differentes cultures dans deux saisons consécutives ont donné des meilleurs résultats plus que la plantation d'une même culture. La patate douce, qui est une des principales cultures vivrières de cette région où l'essai a été conduit a été trouvée être une culture de rotation diminuant la bactériose. Les haricots, principale culture vivrière et une source de protéines, mais probablement moins transporteur de Ralstonia solanacearum, peut être une culture de bonne rotation, si il est utilisé avant ou après les céréales dans un programme de rotation de la pomme de terre.

Mots Clés: Rotation des cultures, infestation, rendememnt commercialisable, Solanum tuberosum, ware potatoes, incidence du mildiou

INTRODUCTION

Bacterial wilt (BW) caused by Ralstonia solanacearum is an important potato disease in the highlands of southwestern Uganda. In Kabale, a major potato district in southwest Uganda, BW is the second most important disease after late blight and accounts for 30% crop losses (Alacho and Akimanzi, 1993) with occasional losses of 100% if severe attack occurs early in the growth period (Kakuhenzire et al., 1993). A more recent survey (Lemaga et al., 1999) indicated that farmers in Kabale lose 26% of their potato yields to BW and fear that it will be the single most important threat to potato production if appropriate control measures are not made available in near future. Low (1997) expressed a similar concern.

Build-up of the disease is exacerbated by declining soil fertility due to intensive cultivation as a result of high population density (Low, 1997), favourable highland climate and use of infected seed (Verma and Shekhawat,1991; Tusiime et al., 1996), all of which are the case in the highlands of south western Uganda.

Several research reports indicate that crop rotation helps to significantly reduce or even eradicate potato bacterial wilt and it is recommended as a component of integrated control measure Kloos et al. (1991). It is generally established that in addition to breaking the cycles of insect pest and disease, crop rotation helps to increase productivity of the soil through maintenance of desirable soil structure and fertility. In Australia a two and a half-year rotation with pasture coupled with healthy seed tuber and effective quarantine procedures was sufficient to eradicate potato BW (Lloyd, 1976).

In Rwanda, a two-year rotation helped to produce healthy tubers in the presence of the disease (Van der Zaag, 1986). Verma and Shekhawat (1991) in India also reported that a five-year rotation that included wheat, lupin and maize reduced wilt and increased yield. Higher potato yields were also obtained under crop rotation in the presence of bacterial wilt in Kenya (Barton et al.,1997). Gunadi et al. (1998) in Indonesia also reported potato wilt reductions after two seasons of rotation with pulses, cereals and root crops. After three seasons, significant increases in total yields as well as proportions of marketable to total yields were recorded with rotation treatments as compared to the control. On the other hand, Granada and Sequeira (1983) indicated that crop rotation could be far less useful for the control of bacterial wilt, particularly race 1 than was generally believed. This is because of the diverse nature of the organism and its ability to survive for a long time by infecting roots of non-host plants used in crop rotation (Granada and Sequeira, 1983; Sunaina et al., 1989; Shekhawat et al., 1990). Jackson and González (1981) reported that on naturally infested soil, rotations with maize, cowpeas, and sweetpotatoes did not reduce the relative inoculum potential of Pseudomonas solanacearum, race 1. At the location where this experiment was done, Tusiime et al. (1996b) asserted that many herbaceous weeds were latently infected with the bacterium increasing its survival in the absence of potatoes. Survival of the pathogen for long periods in the absence of the host was shown by Sunania et al. (1989) and Alcalá et al. (1998).

In the highlands of southwestern Uganda, a diversity of crops: pulses, cereals, vegetables and root crops are grown. These crops are often rotated with potato but a systematic pattern that could reduce bacterial wilt with eventual aim of eradication has not yet been determined. This study was therefore set up to determine the effects of one- and two-season rotations with some cereals, pulses, root crops and vegetables on BW incidence and tuber yields; identify appropriate rotation crops and planting sequences to reduce BW incidence.

MATERIALS AND METHODS

The experiments were conducted between 1995B and 1999A seasons at the Agricultural Research and Development Centre, Kachwekano (01°16' S, 29° 57' E) at an altitude of 2,200 metres on soils classified as isomesic typic palehumult (Yost and Eswaran, 1990). Prior studies showed that BW in Kabale district, where the experiment was conducted is caused by R. solanacearum, race 3 only. Thus the findings of this study hold true for this race. The area has a rugged terrain with hillside farming done on developed terrace benches. The rainfall is bimodal with a mean of about 1000 mm per annum. Mean maximum and mean minimum temperatures are 23°C and 10°C, respectively. Wide variations in weather, particularly rainfall were experienced during the experimental period (Table 1).

In the seasons preceding the experiments, the fields were planted to a BW susceptible variety Kabale (CIP-374080.5) to uniformly increase the inoculum pressure. Where uniformity was lacking, healthy plants were artificially inoculated by a stem-puncture method. Two fields that exhibited different levels of BW incidence on the susceptible variety were used for the different sets of experiments. One of the fields exhibited an initial incidence of over 90% (heavily infested) with a uniform distribution and the other 15-20% (mildly infested) also with uniform distribution. One set of one-season and the two-season rotation trials were planted in heavily infested field and the second set of one-season rotation trial was planted in mildly infested field. Due to the poor fertility of the heavily infested soil, N: P: K at a rate of 50:40:40 about half dose of the blanket recommendation for potatoes was applied to potatoes, maize and wheat, while beans received 25:20:20. The NPK sources respectively were urea, single super phosphate and murate of potash.

Crops that are commonly grown in the area were included in the treatments (Table 2) with the exception of sorghum. Although sorghum is one of the most widely grown crops in the area, it was not included because of its long maturity period, which wouldn't allow two plantings in a year.

The experiments including initial planting of the fields to a susceptible variety were carried out between 1995B and 1999A seasons all in a randomised complete block design with 4 (one set of one-season and the two-season experiments) and 3 replications for one set of one season experiments. In the one season experiments, the test variety Victoria was planted after a rotational crop, while in the two-season experiments, two different rotational crops or the same crop were grown in two consecutive seasons. The potato variety Victoria (381381.20) originated from the International Potato Centre (CIP) and released by the National Agricultural Research Organisation (NARO) was used for all trials, while local varieties were used for the rotation crops. All the crops were planted at recommended spacings, which for potatoes was 75 x 30 cm. late blight was controlled with Dithane-M45 and ridomil-MZ, as the need arose, each of which was sprayed at recommended rates.
Assessment of the bacterial wilt disease started with the onset of wilt symptoms, after which counting of wilted plants was done on a weekly basis. Plants that showed either complete or partial wilting were all considered wilted and staked to avoid double counting in subsequent assessments and also to avoid the possibility of missing out those that completely die early in the growth period. Wilt incidence for each treatment was then calculated as percentage of total number of plants emerged. For statistical comparisons, percent wilt incidences were transformed into square roots before analysis.

Tubers were harvested after about 75% of the plants reached senescence. At harvest, total and marketable yields were separately determined. Since latent BW infection was not tested, yields in this publication refer to ware potatoes. Data were statistically analysed using Genstat 4.23 Release.

RESULTS AND DISCUSSION

One-season rotation. In a highly infested field (>90% infestation), a one-season rotation with maize and wheat reduced the wilt incidence by approximately 18% and significantly increased total tuber yields as compared to the control (Table 3). Marketable yield differences of 3.2, 2.7 and 2.4 t ha-1 were obtained over the control after rotation with maize, wheat and beans, respectively. This result is consistent with the findings of Devaux et al. (1987) and Kloos et al. (1991), who reported significant reductions in wilt in a one- season crop rotation. The control treatment did not only result in low total yields but also in the lowest proportion of marketable to total yields, which agrees with the report of Verma and Shekhawat (1991). The negative effects of rotation crops on BW may be associated, among others, with a decrease in virulent R. solanacearum population (Kloos et al., 1991; Abd El-Ghafar, 1998; Gunadi et al., 1998) and an increase in avirulent population (Abd El-Ghafar, 1998) as well as the presence of antagonistic bacteria in their rhizospheres as was indicated by Elphinstone and Aley (1992) for maize. They reported that the presence of Psuedomonas cepacia, which is antagonistic to R. solanacearum, in the rhizosphere of maize could be responsible for reduced BW in a potato-maize rotation. The finding of this report does not seem to comply with that of Jackson and González (1981), who reported that rotations with maize, cowpeas and sweetpotatoes did not reduce the populations of the pathogen. The discrepancy might have ensued from different races of the pathogen dealt with in these two studies. This study dealt with race 3, while that of the above authors with race 1.

Although rotation with beans did not significantly increase potato yields, it resulted in total and marketable yield increases of 219% and 300%, respectively (Table 3). The corresponding increases for maize and wheat were respectively 312 and 300% for total yields and 400 and 338 % for marketable yields. Generally, yields were very low due mainly to high wilt incidence, and this is supported by the negative relationship (R2=0.93) between wilt incidence and yield (Fig. 1), which substantiates the findings of Devaux et al.(1987). A unit increase in bacterial wilt incidence resulted in a proportionate decline in marketable yield by about 16%. This re-affirms the economic importance of wilt in production of potato in the highlands of Kigezi (Kakuhenzire et al.,1993; Low,1997; Lemaga et al.,1999; Adipala et al., 2000). Since beans, the most important food crop and a major source of plant protein in Kabale (Low, 1997; Berga et al., 1999) is reportedly a symptom less carrier of the bacterium (Granada and Sequeira, 1983; Kloos et al., 1991; Kishore et al., 1994), it may not be advisable to use it as a sole rotation crop for potatoes.

Table 3 also shows that rotation did not influence days to onset of wilt implying that in this particular case rotation differentially affected wilt progress after its onset. This may be attributed to reduced R. solanacearum population after rotation as compared to potato monoculture (Kishore et al., 1994; Abd El-Ghafar, 1998).

In the mildly infested field (15 - 20% infestation), all the one-season rotations with pulses, cereals, vegetables and root crops, although not different from one another, significantly decreased BW incidence and increased potato marketable yields (P<0.01) when compared with the control (Table 4). On average, total yields from a mildly infested field (Table 4) were more than three times superior to those from a highly infested field (Table 3) restating the negative relationships between the intensity of BW incidence and resultant tuber yields (Devaux et al., 1987; Verma and Shekhawat, 1991). Although lowest BW incidences were recorded after rotations with finger millet (3.2%) and sweetpotatoes (3.8%), yields were lowest with these treatments and highest under rotations with carrots and onions that suffered a wilt incidence of 11 and 12.4%, respectively. It can thus be speculated that apart from reducing BW incidence in crop rotation, it may be important to also consider the fertility implications of crops included in the rotation. In this particular case it seemed that the heavy competition posed by finger millet and sweetpotatoes for soil nutrients had an overriding influence on potato yields than the result effect of reduced BW incidence on yield. It may thus be advantageous to fertilise the soil for high tuber yields whenever potatoes follow such heavy feeders as sweetpotatoes and finger millet. It is, however, important to note that sweetpotatoes, the second most important food crop in Kabale (Low, 1997; Lemaga et al., 1999) reduced BW incidence caused by race 1 of the bacterium which is contrary to the reports by Jackson and Gonz ález (1981). Similarly, although rotations with shallow-rooted crops such as carrots and onions suffered relatively high wilt incidences, the resultant yields were high. These results support the findings of Gunadi et al.(1998) who reported high yields after carrot. The high yields could probably be explained by little exploitation of soil nutrients by these crops at lower soil depths of 15-30 cm, where the potato is apparently active. Research has shown that tuber yields increase with application of soil amendments in areas where this rotation experiment was conducted (Lemaga et al.,2001 this issue).

Two-season rotation. Days to onset of BW were not affected by the different treatments. However, after onset of wilt at 40 days after planting (DAP), progress of BW was fastest and highest with the potato monoculture (control) resulting in wilt incidence of 81% at 91 DAP (Fig. 2). All the two- season rotations reduced bacterial wilt incidence but planting two different crops was superior to planting the same crop in two subsequent seasons in a rotation. The progresses of wilt with time as well as total wilt incidence were both lowest with potato - beans - maize - potato and potato-wheat-maize-potato treatments. Highest and rapid progress of BW in potato monoculture could be attributed to increases in pathogen population (Kloos et al., 1991, Kishore et al., 1994; Abd El-Ghafar, 1998; Gunadi et al., 1998). With all treatments, wilt progress was fastest between 40 and 68 DAP, after which the progress increased at a decreasing rate up to 89 DAP. There was a slight increase in wilt progress between 89 and 96 DAP, but this may have been due to senescence. Since BW is a systemic disease, it spreads fast when plants are most active and cell walls are still tender enough for penetration, and this justifies the early rapid progress observed in this study.

After a two-season rotation, wilt incidence was reduced from 81% in the monoculture check to less than 50%, which was significant at P<0.05 (Table 5). This complies with the findings of Verma and Shekhawat (1991), who in a five-year rotation of potato-wheat-lupin-maize-potato recorded a wilt incidence of 6.3% as compared to 80.1% in the potato monocrop. Rotations that included beans followed by cereals or those that had two different cereals performed best. The treatment potato-beans-maize resulted in the lowest BW incidence of 21.9% that differed significantly from all other treatments, except for potato-wheat-maize potato (25.2%) and potato-beans-wheat-potato (36.4%). Planting non-solanaceaus crops during one, two or three growing seasons in rotation has been found to reduce potato BW incidence (Kloos et al., 1991; Gunadi et al., 1998). Kloos et al. (1991) have reported that in their two- season rotations wilt incidence was reduced by 32% and 24% compared to potato monocrop (88%), in sweetpotato-sweetpotato and maize-sweetpotato rotations, respectively. Bang and Wiles (1995) also reported reduction in wilt incidence following sweet potato in a two-season rotation but found it to be less effective than rotations that included maize because beans are potential host of R. solanacearum (Granada and Sequeira, 1983). Rotations including maize in one season have particularly been found to be more effective in reducing wilt incidence (Kishore et al., 1994; Bang and Wiles, 1995). This could be attributed to the presence of the antagonistic P. cepacia to R. solanacearum (Elphinestone and Aley, 1992). This seems to suggest that planting pulses like beans followed by maize could be a potential strategy to reduce BW of potato.

All the treatments resulted in significantly higher total and marketable ware yields as compared to the potato monoculture, but without significant differences among themselves (Table 5). Marketable yield increases over the control ranged from 216 to 400%. The control treatment also had the lowest proportion (58%) of marketable yields of the total indicating that not only the quantity was lowest with monoculture but also the quality of tubers produced was the poorest. Increase in yields by all the treatments is mainly because they all significantly (P<0.05) reduced bacterial wilt. The crops included in this rotation can potentially be used in the rotation cycles. However, better results can be obtained if pulses follow cereals in rotations (Kishore et al., 1994; Bang and Wiles, 1995). It is highly likely that apparently healthy tubers harvested after crop rotation on infested soils can be latently infected (Graham et al., 1979; Sunaina, 1989; Tusiime et al., 1996b) that can spread the disease.

CONCLUSIONS AND RECOMMENDATIONS

Crop rotation has a potential to reduce but not eradicate BW in short-season rotations, particularly if the field is heavily infested. One-season rotations did not reduce BW nor increase potato yields to acceptable levels on heavily infested soils, but were successful on mildly infested soils. On heavily infested soils, two-season rotations with two different crops, a legume such as beans (the main food crop in the study area) followed by a cereal such as maize was found effective in significantly reducing BW and increasing ware yields. Beans alone are not a good rotation crop where BW is important. Sweetpotato, which is a very important food security crop, was also found effective in reducing wilt incidence when included in potato rotation. However, for high tuber yields it is advisable to fertilise the soil whenever potato follows a sweetpotato.

We strongly suggest that for effective and economically sound potato production in areas with a BW problem, crop rotation be considered as an important component of an integrated control option. Whenever potatoes from rotation trials are used for seed, latent infection be tested using an NCM-ELISA kit developed by CIP. We also suggest that future research should target identification of non-host crops that could be used in rotations and their effects on soil Ralstonia solanacearum population studied.

ACKNOWLEDGEMENTS

This experiment was part of the activities of the integrated pest management of the African Highlands Initiative (AHI). It was funded by AHI through the International Potato Centre (CIP). We also thank P. Ebanyat and D. Siriri for their help in data analysis. We are also indebted to Drs. P. Ewell, S. Priou and E.R. French for their techical support.

REFERENCES

Abd El-Ghafar, N.Y. 1998. Control of potato bacterial wilt using crop rotation. Annals of Agricultural Science 43:575-587.

Adipala, E., Namanda, S., Mukalazi, J., Abalo, G., Kimoone, G. and Hakiza, J.J. 2000. Farmer potato varietal selection criteria in Uganda. African Potato Association Conference Proceedings 5: (in press).

Alacho, F. O. and Akimanzi, D.R. 1993. Progress achivements and constraints on bacterial wilt control in Uganda. In: Workshop proceedings on bacterial wilt of potato caused by Psuedomonas solanacearum, Bujumbura, Burundi, 23-23 February1993. pp. 32-41.

Alcalá, de M.D. and Betsy, L. 1998. Estudio de la marchitez bacteriana de la papa en tres localidades del estado lara. Agronomia Trop. 48:275-289.

Bang, S.K. and Wiles, G.C. 1995. Control of bacterial wilt (Psuedomonas solanacearum) in potato by crop rotation. In: SAPRAD on the Third Year of Phase III. Rasco, Jr. E.T. and Aromin, F.B (Eds.), pp. 103-106 .Selected Research Papers Vol 1. South Asian Program for Potato Research. Manila, Philippines.

Barton, D., Smith, J. and Murimi, Z.K. 1997. Socio-economic inputs to 'biological control of bacterial wilt diseases of potato in Kenya'. ODA RNRRS Crop protection: R66292 (NR International: ZA0085), 22 pp.

Berga Lemaga, Siriri, D. and Ebanyat, P. 2001. Effect of soil amendments on bacterial wilt incidence and yield of potatoes in southwestern Uganda. African Crop Science Journal 9:267-278.

Devaux,A., Michelante, D. and Bichumpaka, M. 1987. Combination of rotation and resistance to control of bacterial wilt (Psuedomonas solanacearum) in Rwanda. Pp 100-101. EAPR Abstracts. Tenth Triennial Conference of European Association for Potatao Research, Aolborg, Denmark.

Elphinstone, J.G. and Aley, P. 1992. Integrated control of bacterial wilt of potato in the warm tropics of Peru. In: Bacterial wilt Proceedings No 45. Hartman, G. L. and Hayward, A.C. (Eds.), pp. 276-283. Kaoshuing, Korea.

Graham, J., Jones, D.A. and Lloyd, A.B. 1979. Survival of Pseudomonas solanacearum Race 3 in plant debris and in latently infected potato tubers. Phytopathology 69:1100-1103.

Granada, G.A. and Sequeira, L. 1983. Survival of Pseudomonas solanacearum in soil, rhizosphere, and plant roots. Canadian Journal of Microbiology 29:433-440.

Gunadi, N., Chujoy, E. Kusmana, M., Surviani, I., Gunawan, O. S. and Sinung- Basuki. 1998. Effect of crop rotation patterns on Ralstonia solanacearum population in the soil. Potato reseach in Indonesia. Results in working paper series, CIP/RIV. pp. 56-61.

Jackson, M.T. and González, L.C. 1981. Persistence of Pseudomonas solanacearum (Race 1) in a naturally infested soil in Costa Rica. Phytopathology 17: 690-693.

Kakuhenzire, R., Alacho, F., Birikunzira, J., Turyamureeba, G. and Sikka, L. 1993. Progress in field evaluation for resistace to Psuedomonas solanacearum and cultural methods for control of bacterial wilt in Uganda. pp. 76- 82. In: Proceedings of a workshop on bacterial wilt. Bujumbura, Burundi. 22-26 February 1993.

Kishore, V., Sunaina, V. and Shekhawat, G.S. 1994. Relative effectiveness of various crop rotations on incidence of potato bacterial wilt. In: Proceedings of Potato: Present and future. Shekawat, G.S., Khurana, S.M. P., Pandey, S.K. and Chandla, V.K. (Eds.), pp.184-187. Indian Potato Association. Shimla, India.

Kloos, J.P., Fernandez, B.B., Tumapon, A.S. and Villanueva, L. 1991. Effects of crop rotation on incidence of potato bacterial wilt caused by Psuedomonas solanacearum E.F. Smith. Asian Potato Journal 2:1-3.

Lemaga, B., Hakiza, J.J., Bariyanga, J. and Ewell, P. T. 1999. Potato production and importance of potato bacterial wilt in Kabale district, southwestern Uganda: A farm survey report. African Highlands Initiative/International Potato Center 40 pp.

Lloyd, A. B. 1976. Bacterial wilt in cold- temperature climate of Australia. In: Planning Conference and Workshop on ecology and Control of bacterial wilt caused by Psuedomonas solanacearum. North Carolina state University, Raleigh, North, Carolina. pp. 134 -135.

Low, J.W. 1997. Potato in southwestern Uganda. Threats to sustainable production. African Crop Science Journal 5:295-412.

Shekhawat, G.S., Bahal, V.K., Kishore, V., Sanger, R.B.S., Patel, R.L., Dey, B.K., Sinha, S.K. and Pani, A.K. 1990. Control of bacterial wilt of potatoes by agronomic practices. Indian Potato Association 17:52-60.

Sumaina, V., Kishore, V. and Shekhawat, G.S. 1989. Latent survival of Pseudomonas solanacearum in potato tubers and weeds. Journal of Plant Diseases and Protection 96:361-364.

Tusiime, G., Adipala, E. Opio, F. and Bhagsari, A.S., 1996. Occurrence of Pseudomonas solanacearum latent infection in potato tubers and weeds in highland Uganda. African Journal of Plant Protection 6:108-118.

Van der Zaag, P. 1986. Potato production under Psuedomonas solanacearum conditions: Sources and management of planting material. In: Proceedings of Bacterial disease in Asia and South Pacific. Proceedings No 13. Canberra, Australia. pp. 84-88.

Verma, R.K. and Shekhawat, G.S. 1991. Effect of crop rotation and chemical soil trteatment on bacterial wilt of potato. Indian Phytopathology 44:5-8.

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TABLE 1. Mean monthly maximum and minimum temperatures and monthly rainfall for Kabale during 1995-1999
Months
Temperatures (°C)
Rainfall (mm)
1995
1996
1997
1998
1999
1995
1996
1997
1998
1999

Max.

Min.

Max.

Min.

Max.

Min.
Max.
Min.
Max
Min.

Jan.

24.8

11.2

24.1

10.9

23.9

11.8

24.2

13.0

24.0

11.4

44.7

70.2

101.4

183

76.6

Feb

24.0

11.4

23.8

11.3

25.8

10.5

24.7

13.3

26.2

10.4

127.8

57.0

<0.1

96.7

36.0

Mar.

22.7

12.0

24.1

11.9

24.3

11.8

25.3

13.0

23.6

11.9

105.4

146.0

113.8

101.2

144.9

Apr.

22.9

11.9

23.6

12.3

23.2

12.9

24.3

13.6

23.5

11.8

82.4

92.9

122.4

171.3

71.6

May

23.5

12.9

22.9

12.5

23.3

12.3

23.8

13.3

23.1

10.9

147.4

45.5

148.8

169.6

1.4

Jun.

23.8

11.7

23.0

11.9

23.8

10.6

25.4

10.9

24.5

9.8

122.7

71.7

32.8

18.5

0

Jul.

23.7

10.3

23.3

10.0

23.9

10.4

24.3

10.0

1.2

50.3

27.0

19.8

Aug.

25.7

9.8

24.5

10.2

25.5

11.5

25.0

10.6

5.5

117.8

36.9

23.1

Sep.

25.0

11.7

24.5

11.8

27.2

10.6

25.2

11.1

114.1

122.9

24.8

87.4

Oct.

23.2

12.3

23.8

12.4

25.1*

12.5

25.1

12.8

165.6

144.0

155.1

154.2

Nov.

24.0

12.3

23.2

12.2

-

13.3

24.5

12.1

104.7

201.6

195.8

58.4

Dec.

23.4

10.6

23.9

11.9

23.1

13.0

24.3

10.4

102.5

102.5

150.8

80.0

Source: Department of Meteorological Observation, Kabale
* Average of the first ten days of the month. Due to a damage caused to the thermometer, data were not taken for the rest of October
- Data not available

TABLE 2. Treatments used in the rotation experiments

One-season rotation Two-season rotation

Set 1

1. Potato-maize-potato

1. Potato-beans-wheat- potato

2. Potato-wheat-potato

2. Potato-beans-maize potato

3. Potato-beans-potato

3. Potato-wheat-maize potato

4. Potato-potato-potato

4. Potato-beans-beans potato

5. Potato-maize-maize potato

Set 2

6. Potato-wheat-wheat potato

1. Potato-onions-potato

7. Potato-potato-potato potato

2. Potato-peas-potato

3. Potato-cabbage-potato

4. Potato-sweet potato-potato

5. Potato-millet-potato

6. Potato-carrots-potato

7.Potato-beans-potato

8. Potato-potato-potato

TABLE 3. Effects of one-season rotation on days to onset of BW incidence, percent bacterial wilt incidence and potato yields at Kachwekano, 1996B season

Treatment

Days to onset of BW symptom
Wilt incidence (%)
Total yield (t ha-1)
Marketable yield (t ha-1)
% increase in marketable yield
% marketable yield of total

Potato-maize-potato

42

79.4 (8.86)*

6.6

4.0

400

60.6

potato-wheat- potato

42

79.3(8.88)

6.4

3.5

338

54.7

potato -beans- potato

40

80.9(8.94)

5.1

3.2

300

62.7

potato - potato P- potato

40

97.1(9.85)

1.6

0.8

-

50.0

LSD (0.05)

NS

(102)

3.9

2.9

* Figures in parenthesis are square roots
NS= not significant

TABLE 4. The effect of one-season rotation with various crops on bacterial wilt incidence at Kachwekano, 1999A

Treatment

Bacterial wilt incidence (%)
Total yield (t ha-1)
Marketable yield (t ha-1)
% increase in marketable yield
% marketable yield of total

Potato-Onions- potato

12.4 (3.5b)*

20.4a

20.0a

80

98

Potato-Peas - potato

5.0 (2.2b)

18.6a

18.5a

67

99

Potato-cabbage – potato

6.9 (2.61b)

17.7a

17.6a

59

99

Potato-sweetpot.-potato

3.8 (1.57b)

16.4ab

16.4a

48

100

Potato-millet- potato

3.2 (1.7b)

16.7ab

16.7a

50

100

Potato-carrots – potato

11.0 (3.3b)

20.4a

20.4a

84

100

Potato-beans –potato

7.4 (2.2b)

18.1a

18.1a

63

100

Potato-potato-potato

62.2 (7.8a)

12.4b

11.1b

-

90

* Figures in parenthesis are square roots. Means followed by same letters in columns are not significantly different at 5% probability level

TABLE 5. Effect of two-season rotation on bacterial wilt incidence and potato yields at Kachwekano, 1997A season

Treatment

Wilt incidence (%)
Total yield (t ha-1)
Marketable yield (t ha-1)
% increase in marketable yield
% marketable yield of total

Potato-Beans -Wheat-Potato

36.4 (5.81 bcd)*

9.27a

7.40a

300

80

Potato-Beans –Maize-Potato

21.9 (4.52 d)

10.37a

9.00a

386

87

Potato-Wheat-Maize-Potato

25.2 (4.89cd)

10.7a

8.90a

381

83

Potato-Beans-Beans-Potato

40.3 (6.32bc)

8.92a

6.68a

216

75

Potato-Maize-Maize-Potato

49.4 (7.01b )

10.15a

8.40a

354

83

Potato-Wheat-Wheat-Potato

40.0 (6.28 bc)

10.73a

9.23a

400

86

Potao-Potato-Potato-Potato

81.1 (8.96 a)

3.20b

1.85b

-

58

LSD(0.05)

(1.47 )

2.72

2.41

* Square root values
Means followed by same letters are not significantly different using Duncan's Multiple Range Test

Figure 1. Relationship between marketable yield and bacterial wilt incidence (1996B).

Figure 2. Effect of a two-season rotation with cereals and beans on bacterial wilt development (1997A).


The following images related to this document are available:

Line drawing images

[cs01056a.gif] [cs01056b.gif]
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