QTL Mapping of Traits Associated with Dual Resistance to the African Stem Borer (Busseola fusca) and Spotted Stem Borer (Chilo partellus) in Sorghum (Sorghum bicolor)

Sorghum (Sorghum bicolor (L.) Moench) is an important food crop in semi-arid tropics. The crop grain yield ranges from 0.5 t/ha to 0.8 t/ha compared to potential yields of 10 t/ha. The African stem borer Busseola fusca Fuller (Noctuidae) and the spotted stem borer Chilo partellus Swinhoe (Crambidae), are among the most economically important insect pests of sorghum. The two borers can cause 15% - 80% grain yield loss in sorghum. Mapping of QTLs associated with resistance traits to the two stem borers is important towards marker-assisted breeding. The objective of this study was to map QTLs associated with resistance traits to B. fusca and C. partellus in sorghum. 243 F9:10 sorghum RILs derived from ICSV 745 (S) and PB 15520-1 (R) were selected for the study with 4,955 SNP markers. The RILs were evaluated in three sites. Data was collected on leaf feeding, deadheart, exit holes, stem tunnels, leaf toughness, seedling vigour, bloom waxiness, and leaf glossiness. ANOVA for all the traits was done using Genstat statistical software. Insect damage traits and morphological traits were correlated using Pearson’s correlation coefficients. Genetic mapping was done using JoinMap 4 software, while QTL analysis was done using PLABQTL software. A likelihood odds ratio (LOD) score of 3.0 was used to declare linkage. Joint analyses across borer species and sites revealed 4 QTLs controlling deadheart formation; 6 controlling leaf feeding damage; 5 controlling exit holes and stem tunneling damages; 2 controlling bloom waxiness, leaf glossiness, and seedling vigour; 4 conditioning trichome density; and 6 conditioning leaf toughness. Joint analyses for B. fusca and C. partellus further revealed that marker CS132-2 colocalised for leaf toughness and stem tunneling traits on QTLs 1 and 2, respectively; thus, the two traits can be improved using the same linked marker. This study recommended further studies to identify gene(s) underlying the mapped QTLs.

Evaluation of Aqueous Extracts of Neem kernels and leaves for the control of spotted stem borer Chilo partellus Swinhoe, in sorghum at New Halfa, Sudan

A field experiment was conducted to study the effect of different concentrations of aqueous extracts of Neem kernels (NK) and Neem leaves (NL) on the incidence and damage of spotted stem borer in sorghum during 2011/12-2012/13 seasons at New Halfa Research Station farm. Sorghum variety Tabat was used. The experiment was laid in a RCB design with four replicates and seven treatments. These were: NK at kg/ 30 and 40 Liter of water, NL at kg/15 and 20 Liter of water, Furadan10% G at 15kg/F and Malathion 57% EC at 2L/F as standard and the untreated control. A liquid soap was added to Neem treatments as an emulsifying agent. Three sprayings were applied using knapsack sprayer starting two weeks after emergence with 10 days intervals. Data on percent deadheart, percent leaf damage plants, percent stem tunneling, number of borer holes per plant and grain yield were recorded. Results indicated that, all treatments were highly significantly (P>0.001) reduced stem borer damage and increased the grain yield compared to the untreated one. NK at kg/ 40 L of water was the best in reducing stem borer damage and increasing grain yield comparable to the standard treatment Furadan 10% G at 15 Kg/F.

Screening and partial characterization of d-endotoxins from some local Bacillus thuringiensis isolates for insecticidal activity against the spotted stem borer

Kimani PG, Nyambaka H, Kasina M. 2018. Screening and partial characterization of d-endotoxins from some local Bacillus thuringiensis isolates for insecticidal activity against the spotted stem borer. Biofarmasi J Nat Prod Biochem 17: 21-38. Prolonged use of synthetic chemical pesticides is environmentally undesirable, causing the rapid development of resistance among insect pests. Kenya has unexplored potential in controlling lepidopteran pests by using proteinous delta-endotoxins sourced from local isolates of a naturally occurring bacterium, Bacillus thuringiensis Berliner (Bt). This study attempted to identify the insecticidal proteins in some Kenyan Bt isolates, characteristic of Cry1 and/or Cry2 proteins. It also aimed to test their efficacy as affected by different temperatures and their specificity on an invasive and prevalent lepidopteran stem borer, Chilo partellus (Swinhoe). Delta-endotoxin crystals were isolated and purified from cultures of twenty unidentified local Bt isolates using froth floatation and centrifugation. Total protein in the resulting suspensions was quantified using the Bradford assay method, and the approximate protein yield was 3.14 ±0.084 mg/mL of nutrient broth culture with a purity level of 54.8 % ±15.3 %. Leaf-dip bioassays used for testing the efficacy of the d-endotoxins against C. partellus. Among the isolates evaluated, Bt 44 and Bt 48 had the most potent d-endotoxin crystals towards the 1st instar larvae, leading to mortality of 62.6 % and 64.8 % respectively after 72 h. The effect of the d-endotoxins' concentration and temperature on larval mortality was examined for 72 hours at temperatures of 24°C, 27°C and 31°C and levels of 0.01 mg/mL, 0.1 mg/mL and 1.0 mg/mL. The resulting LC50 was 52.3 µg/mL and 42.0 µg/mL, while LT50 values were 76.7h and 60.9h for Bt 44 and Bt 48, respectively. Higher efficacy found at 24°C and 31°C than at 27°C, an indication that these d-endotoxins are tolerable for local conditions where temperatures are higher than in temperate regions. The relationship between concentration and temperature was significant for d-endotoxins of Bt 48 but not those of Bt 44. A major protein component of the d-endotoxins had a molecular weight Mr ~ 130 kDa, which generates a trypsin-resistant core of Mr ~ 70 kDa. Cry protein analysis detected more Cry1 in Bt 44 than Bt 48 ?-endotoxins and no Cry2 in either. However, cry gene analysis using PCR detected the presence of both cry1 and cry2 genes in the DNA of Bt 44 but none in Bt 51, a negative control from toxicity tests against the pest. The chromatographic analysis revealed some differences in the elution profiles of d-endotoxins of both Bt 44 and Bt 48, an indication that there may be different types and amounts of the Cry toxins in the crystals or even novel proteins. These findings indicate that the two local Bt isolates expressed Cry1, and probably Cry2 proteins can control C. partellus and may, therefore, become promising sources for ?-endotoxins for biopesticide development for controlling the pest.