Developing dual-resistant cassava to the two major viral diseases

Cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) are the two important biotic constraints affecting cassava production in sub-Saharan Africa (SSA). Deployment of cassava varieties dually resistant to both diseases is the most effective and realistic way of reducing losses to African farmers. Crosses were carried out between the Tanzanian local cassava variety Namikonga (CBSD resistant/CMD susceptible) with an introduced cassava germplasm AR37-80 (CBSD susceptible/CMD resistant) from South America to develop dually resistant F1 progenies and they were evaluated for 2 seasons at Naliendele in Southern Tanzania which is a CMD and CBSD hotspot area. CMD-resistant progenies had low foliar severities (≤ 1.8 on a five-point scale) similar to CMD resistant parent. CBSD resistant progenies had minimal foliar severity (≤2.0) and root necrosis (≤1.2) similar to the CBSD resistant parent while CBSD tolerant progenies had severe foliar severity of up to 3.3 but minimal root severity (≤ 1.2). Traits with minimal environmental influence also had high heritability (≥0.65) and high selection accuracy (≥0.70) and they included CMD foliar symptoms, CBSD foliar symptoms at 6 MAP, root necrosis, root necrosis incidence, root weight, root number per plant, and harvest index. Correlation analysis showed that the presence of diseases reduces usable roots, root weight, root number per plant, and harvest index. Dual resistance can improve yield as observed in the progenies, Namar 050 and Namar 371 which had high root weights of 27.5 t/ha and 28.2 t/ha with high genetic gains of 56.1% and 58.5%, respectively. Dual resistant progenies identified were Namar 050, Namar 100, Namar 130, Namar 200, Namar 334, Namar 371, and Namar 479 as they had minimal CMD and CBSD symptoms severity (≤ 2.0) and could be used for breeding cassava varieties with superior characteristics

Genotype by environment interactions in identifying cassava (Manihot esculenta Crantz) resistant to cassava brown streak disease

Cassava landraces were evaluated for resistance to cassava brown streak disease (CBSD) for two cropping seasons at a disease hotspot area in Naliendele, Tanzania. Based on reactions to CBSD, several landraces including Chimaje, Mfaransa and Supa B were considered to be resistant to the disease while Kikwada, Mbuyu, and Nyoka were tolerant. ANOVA revealed that the largest sum of squares (SS) (41.9–86.7%) was attributed to the genotype of the cassava landraces, while a smaller proportion of SS (8.1–38.2%) was due to genotype by environment interactions for all traits tested, which included disease symptoms, root weight, number of roots per plant and dry matter content. Environment accounted for the smallest effect (0.01–26.3%), however, the mean squares was nonetheless significant for a few genotypes, which indicated that their disease expression was indeed influenced by the environment. Increased CBSD severity was associated with low temperatures and rainfall. Increased rainfall towards harvesting led to higher root weight but lower dry matter content in the first cropping season. Correlation analysis showed that the presence of CBSD symptoms reduces the amount of usable roots, total root weight, and root dry matter content. Many resistant/tolerant landraces also had high root weight and dry matter content, and they can be used by farmers to reduce CBSD losses. The landraces described here form novel sources of CBSD resistance that can be used for breeding disease-resistant cassava varieties with superior agronomic characteristics

Flowering margins support natural enemies between cropping seasons

IntroductionPopulations of natural enemies of insect pests are declining owing to agricultural intensification and indiscriminate use of pesticides, and this may be exacerbated in agricultural systems that clear all margin plants after the cropping season for other uses such as fodder. Retaining a diversity of non-crop flowering vegetation outside the cropping season may support more resilient and effective natural pest regulation.MethodsWe tested the potential for non-crop vegetation to support natural enemies in fields across two locations after harvesting the primary crops of lablab and maize.ResultsA total of 54 plant species were recorded across the sites in Kenya with 59% of them being annuals and 41% perennials. There was a significant seasonal variation in plant species richness (ANOVA: F1, 16 = 33. 45; P< 0.0001) and diversity (ANOVA: F1, 16 = 7.20; P = 0.0511). While time since harvesting was a significant factor influencing the overall abundance of natural enemies (ANOVA: F2, 1,133 = 8.11; P< 0.0001), they were generally higher in abundance in locations with margin plants or where a diversity of margin plants was observed.DiscussionThese findings demonstrate that flowering plants in agricultural systems offer refuge and alternative food for natural enemies and potentially other beneficial insects between cropping seasons. The conservation of natural enemies between crops may lead to more effective natural pest regulation early in the following crop, thus reducing reliance on insecticides application

Response of Common Bean to Rhizobium Inoculation and Fertilizers

Common bean (Phaseolus vulgaris) yields in Western Kenya are low and this has been attributed to low soil fertility. Field trials were conducted in farmers fields in Ukwala Division of Siaya District in Kenya during the long rains of 1998 and 1999 to determine the potential for improving bean yields through Rhizobium inoculation, and fertilizer N and P applications. The three factors: Rhizobium inoculation at two levels and fertilizers-N and P each at three levels were factorially combined to give 18 treatments. The treatments were laid out in a randomised complete block design with a split-plot structure and three replications. A popular local bean variety Okuodo was used as the test crop. During the 1998 long rains season, P significantly (P=O.05) increased the stand count after emergence, pod number per plant and the bean grain yields. Seed number per plant alone was significantly increased by fertilizer-N application. Significant interaction effects (P=O.05) were observed for NXP on the stand count after emergence and for Rhizobium inoculation XP on stand count after emergence, stand count at harvest and the bean grain yields. Rhizobium inoculation alone did not significantly affect any of the measured variables in both seasons. In 1999, only the bean grain yields were determined and were significantly (P=O.05) increased only by fertilizer P applications. The Journal of Food Technology in Africa Volume 6 No.4, 2001, pp. 121-12

Response of Common bean to Rhizobium inoculation and fertilizers.

Common bean (Phaseolus vulgaris) yields in western Kenya are low and this has been attributed to low soil fertility. Field trials were conducted in farmers fields in Ukwala Division of Siaya District in Kenya during the long rains of 1998 and 1999 to determine the potential for improving bean yields through Rhizobium inoculation, and fertilizer N and P applications. The three factors: Rhizobium inoculation at two levels and fertilizers-N and P each at three levels were factorially combined to give 18 treatments. The treatments were laid out in a randomised complete block design with a split-plot structure and three replications. A popular local bean variety Okuodo was used as the test crop. During the 1998 long rains season, P significantly (P=O.05) increased the stand count after emergence, pod number per plant and the bean grain yields. Seed number per plant alone was significantly increased by fertilizer-N application. Significant interaction effects (P=O.05) were observed for NXP on the stand count after emergence and for Rhizobium inoculation XP on stand count after emergence, stand count at harvest and the bean grain yields. Rhizobium inoculation alone did not significantly affect any of the measured variables in both seasons. In 1999, only the bean grain yields were determined and were significantly (P=O.05) increased only by fertilizer P application

Chemical composition of Cupressus lusitanica and Eucalyptus salignaleaf essential oils and bioactivity against major insect pests of storedfood grains

The leaf essential oils from Cupressus lusitanica, Miller and Eucalyptus saligna, Smith obtained by hydrodis-tillation were analyzed by GC/MS and also screened for their insecticidal and repellent effects against adultTribolium castaneum, Acanthoscelides obtectus, Sitotroga cerealella and Sitophilus zeamais. The C. lusitanicaoil contained mainly umbellulone (18.38%) and �-pinene (9.97%) whereas the E. saligna oil was domi-nated by �-pinene (24.40%) and 1,8-cineole (24.26%). Bioassays showed that of the four insect speciestested, A. obtectus and S. cerealella were the most susceptible to the oils, with LC50values of 0.05–0.11%v/w in contact toxicity and 4.07–7.02 �l/L air in space fumigation. Except in T. castaneum with percentagerepellence (PR) values of 65–92.5%, the other test insects recorded PR values less than 30%. The PR valuesdecreased with exposure time in all insects except in T. castaneum. Our results show that C. lusitanica andE. saligna essential oils are promising insecticides and repellents to be used against insect pests of storedfood grains

Field margins and botanical insecticides enhance Lablab purpureus yield by reducing aphid and supporting natural enemies

Botanical insecticides offer an environmentally benign insect pest management option for field crops with reduced impacts on natural enemies of pests and pollinators while botanically rich field margins can augment their abundance. Here we evaluated the non-target effects on natural enemies and pest control efficacy on bean aphids in Lablab of three neem and pyrethrum based botanical insecticides (Pyerin75EC®, Nimbecidine® and Pyeneem 20EC®) and determine the influence of florally rich field margin vegetation on the recovery of beneficial insects after treatment. The botanical insecticides were applied at early and late vegetative growth stages. Data was collected on aphids (abundance, damage severity and percent incidence) and natural enemy (abundance) both at pre-spraying and post-spraying alongside Lablab bean yield. The efficacy of botanical insecticides was similar to a synthetic pesticide control and reduced aphid abundance by 88% compared to the untreated control. However, the number of natural enemies was 34% higher in botanical insecticide treated plots than in plots treated with the synthetic insecticide indicating that plant-based treatments were less harmful to beneficial insects. The presence of field margin vegetation increased further the number of parasitic wasps and tachinid flies by 16% and 20%, respectively. This indicated that non-crop habitat can enhance recovery in beneficial insect populations and that botanical insecticides integrate effectively with conservation biological control strategies. Higher grain yields of 2.55-3.04 and 2.95-3.23 t/ha were recorded for both botanical insecticide and synthetic insecticide in the presence of florally enhanced field margins in consecutive cropping seasons. Overall, these data demonstrated that commercial botanical insecticides together with florally rich field margins offer an integrated, environmentally benign and sustainable alternative to synthetic insecticides for insect pest management and increased productivity of the orphan crop legume, Lablab

Intercropping and diverse field margin vegetation suppress bean aphid (Homoptera: Aphididae) infestation in dolichos ( Lablab purpureus L.).

Dolichos (Lablab purpureus L.) is a drought tolerant legume used as food/feed and im- provement of soil fertility. The production of dolichos in Kenya, Nakuru County is however limited by insect pests like bean aphids, pod borers and whiteflies. Field stud- ies were conducted to determine the effect of cropping systems (dolichos monocrop and maize-dolichos intercrop) and field margin vegetation on bean aphids and their natural enemies. The experiment was conducted in Njoro (high field margin vegetation) and Ron- gai (low field margin vegetation) during May–December 2019 and March−November 2020 cropping seasons. Bean aphid percent incidence, severity of damage and abundance was assessed at seedling, early vegetative, late vegetative and flowering dolichos growth stages. The populations of natural enemies in the plots and field margin vegetation were monitored using pan traps and sweep nets. Species diversity and composition of the field margin ve-getation was determined using a quadrat. Results showed that location and cropping system had significant effects on bean aphid infestations. A high bean aphid incidence (38.13%) was observed in Njoro compared to Rongai (31.10%). Dolichos monocrop had significantly higher bean aphid infestation (51.63%) than the maize-dolichos intercrop system (24.62%). A highly diverse Shannon-weaver index was observed in Rongai (1.90) compared to Njoro (1.67). Dolichos monocrop had a more diverse Shannon-weaver index (1.8) than the maize- dolichos intercrop system (1.7). Rongai had the most abundant annual and perennial field margin vegetation species. The field margin species richness and diversity were higher in Rongai (81%) than in Njoro (54%). The findings of this study have demonstrated that a maize-dolichos intercrop in Rongai can reduce bean aphid damage in dolichos

Distribution of Puccinia striiformis f. sp. tritici races and virulence in wheat growing regions of Kenya from 1970 to 2014

Stripe rust, caused by the fungal pathogen Puccinia striiformis f. sp. tritici, is a major threat to wheat (Triticum spp.) production worldwide. The objective of this study was to determine the virulence of P. striiformis f. sp. tritici races prevalent in the main wheat growing regions of Kenya, which includes Mt. Kenya, Eastern Kenya, and the Rift Valley (Central, Southern, and Northern Rift). Fifty P. striiformis f. sp. tritici isolates collected from 1970 to 1992 and from 2009 to 2014 were virulence phenotyped with stripe rust differential sets, and 45 isolates were genotyped with sequence characterized amplified region (SCAR) markers to differentiate the isolates and identify aggressive strains PstS1 and PstS2. Virulence corresponding to stripe rust resistance genes Yr1, Yr2, Yr3, Yr6, Yr7, Yr8, Yr9, Yr17, Yr25, and Yr27 and the seedling resistance in genotype Avocet S were detected. Ten races were detected in the P. striiformis f. sp. tritici samples obtained from 1970 to 1992, and three additional races were detected from 2009 to 2014, with a single race being detected in both periods. The SCAR markers detected both Pst1 and Pst2 strains in the collection. Increasing P. striiformis f. sp. tritici virulence was found in the Kenyan P. striiformis f. sp. tritici population, and different P. striiformis f. sp. tritici race groups were found to dominate different wheat growing regions. Moreover, recent P. striiformis f. sp. tritici races in East Africa indicated possible migration of some race groups into Kenya from other regions. This study is important in elucidating P. striiformis f. sp. tritici evolution and virulence diversity and useful in breeding wheat cultivars with effective resistance to stripe rust