BENJAMIN ABOAGYE DANSO
BREEDING GROUNDNUTi[Arachis hypogaea (L.)] FORiRESISTANCE TO LATE LEAFiSPOTS DISEASE IN GHANA
ABSTRACT
Late leafispots disease (LLS) icauses over 70% yieldiloss in groundnutiproduction by ireducing plant areaiavailable foriphotosynthesis. The incidence of LLS have been reported across all the major groundnut producing regions of Ghana. Most groundnut farmers in Ghana do not regard LLS as a disease due to limited knowledge on the disease, hence do not control LLS on their farms. Again, the most popular variety of groundnut in Ghana (Shitouqi) is highlyisusceptible to LLS and this contributes to the low yields that have been recorded in Ghana over the past decade. Breeders in the past have attempted to solve the yield and disease susceptibility problems by introducing new varieties to replace Shitouqi. However, adoption of these new varieties is low partly due to the fact that, the new varieties to not satisfy the needs of the farmers. Most farmers are satisfied with Shitouqi except for its susceptibility to diseases. Conventional method of deploying resistance into an adapted variety takes longer time and requires more resources. Availability of validated markers play important role in reducing the time and cost involved in improving adapted varieties. The objectivesiof this studyiwere first, to identify farmers’ constraints, preferreditraits ofigroundnut and farmers’ perceptions on groundnut diseases; secondly, to validate four Single NucleotideoPolymorphism (SNP) markersilinked to LLS resistance QTL (qLLSA02); thirdly, to identifyinew sources of LLS resistanceoin Ghana’s groundnutigermplasm; and lastly, to introgress LLS resistance QTL (qLLSA02) into Shitouqi groundnut variety. Constraints of groundnut production, perceptions of farmers on groundnut diseases and farmers’ preferred traits of groundnut were established through participatory rural appraisal techniques [focal groupodiscussions (FGD) and administrationoof semi-structured questionnaire]. Seven FGDs were held across three agro-ecological zones that form the groundnut basin of Ghana. From the PRA, participants identified LLS as the most common disease and groundnut rosette virus disease (GRD) as the most important disease. Majority of the respondents ranked groundnut diseases as their most important constraint, followed by low yield, pest and drought. Farmers’ preferred groundnut traits identified in this study included high yield, brittle shell, sweet taste, early maturity, erect growth habit, high oil content, drought tolerance, tan seed colour and tolerance to pests and diseases. Most of the claims made by FGD groups were confirmed using the survey. Results from the survey further revealed that many groundnut farmers (82%) considered LLS as a sign of maturity and not a disease. Only 8% of the respondents had a way of managing LLS on their farms. However, about 95% of the respondents were ready to accept improved varieties that addresses their challenges. On SNP marker validation, 188 F2 plants derived from a cross between LLS resistant CS16 and LLS susceptible Shitouqi were genotyped with four SNP markers proposed to be linked to LLS resistance in groundnut. Phenotypic data (LLS severity score) was taken on F2:3 families derived through selfing F2 lines. Polymorphism test revealed that marker GKAMA02GL779 could not distinguish between the two divergent parents, hence was excluded from further analysis. Single marker analysis using Kruskal-Wallis analysis of variance and linear regression, both established strong association between three SNP markers (GKAMA02GL582, GKAMA02GL829 and GKAMA02GL975) and LLS resistance with adjusted R2 values of 0.758, 0.73 and 0.613, respectively. The three validated SNP markers were then used to identify 13 groundnut accessions that possessed the qLLSA02 QTL. Ten (10) out of the 13 groundnut accessions further showed resistance in a field trial held in three hotspot environments in Ghana – Manga, Fumesua and Nyankpala. Using the three validated SNP markers as foreground markers, a marker assisted backcrossing (MABC) programme was initiated to introgress qLLSA02 loci into the farmer preferred variety, Shitouqi. CS16 variety was used as the donor variety while Shitouqi served as recurrent parent. Seeds with heterozygous genotypes at the three LLS loci marker loci were selected at F1 (30), BC1F1 (37), BC2F1 (13) and BC3F1 (19) generations. At BC3F1, 93.8% of the genome of Shitouqi had been reconstructed. Further selections and evaluations will see to the complete improvement of Shitouqi. Information obtained from the PRA will serve as a baseline for interventions aimed at managing groundnut diseases and increasing yield of groundnut in Ghana. The three validated SNP markers identified in this research can also be used in future breeding programmes to identify LLS resistant lines.