Effects of major fungal diseases on performance of sorghum germplasm under field trials in KALRO Kiboko and Ithookwe in lower eastern Kenya

Abstract

Sorghum is a vital cereal crop especially in the ASALs of Kenya with potential of reducing food insecurity. It’s uses range from food for human consumption, feeds for livestock and as raw materials in industrial processes. However, its potential production is limited by fungal diseases. Therefore, this study aimed at assessing the effects of major fungal diseases on growth and yield of selected sorghum germplasm through field trials. enhanced management of fungal diseases. Fourteen sorghum germplasm, including eight improved genotypes bred for drought tolerance, yield improvement and grain quality improvement from ICRISAT and six local land races from farmers, were subjected to a two-season field experiment laid out in Randomized Complete Block Design (RCBD) with four replications conducted at sub-centers of KALRO (Kiboko and Ithookwe) located in different AEZs of Kenya's ASALs. Natural infection of sorghum germplasm involved use of fungal-infected spreader rows. Sorghum plants were sampled from the first to the fourth month to record disease incidence and severity, identify major fungal pathogens, and determine their effects on growth (plant height, number of green leaves, leaf area and days to 50% flowering) and yield (biomass yield, grain yield, grain weight) parameters. At soft dough stage, symptomatic leaf samples were collected and taken to the laboratory for isolation and identification of fungal pathogens by both morphological and molecular methods. Major fungal diseases and their severity scores at KALRO, Kiboko were: leaf blight (6.1), anthracnose (5.5), rust (5.3), gray leaf spot (3.1), oval leaf spot (2.6) ladder leaf spot (2.1), downy mildew (2.3) and covered kernel smut (1.1), while at KALRO, Ithookwe, were: 4.8, 5.6, 4.6, 1.8, 1.6, 1.4, 2.1 and 1.1, respectively. Major fungal pathogens isolated included: Fusariuum spp, Curvularia spp, Alternaria spp, Bipolaris spp, Exerohilum spp, Colletotrichum spp and Epicoccum spp. Phylogenetic analysis revealed representative isolates as: Curvularia akaiiensis, Curvularia lunata, Bipolaris secalis, Exserohilum rostratum, Fusarium napiforme, Alternaria alstroemeriae (two isolates) and Epicoccum sorghinum. Two improved genotypes (Makueni local and Kiboko local 2) recorded, higher: plant height, days to 50% flowering, number of green leaves, leaf area and dry biomass compared to other germplasm. Significant (P≤0.001) negative correlations were observed between FDS and days to 50% DFL (r= -0.741), STG (r= -0.813) and LA (r= -0.543) indicating that fungal diseases inhibited sorghum growth. Correlations between FDS and yield data (DBM, GRY and GRW) were also negative but insignificant (P>0.05). Seven improved genotypes (Makueni Local, Kiboko Local 2, IESV 24029 SH, Marcia, KARII Mtama 1, Serena and Seredo) showed the least mean FDS scores across several diseases and had significantly higher GRY (1.9 - 2.8 t/ha) compared to local varieties that showed higher FDS and lower yield (<1.9 t/ha). Future studies need to: focus on evaluating and developing biocontrol methods to manage fungal pathogens infecting sorghum crops in lower Eastern Kenya. Improved varieties from ICRISAT that are superior to local landraces should be tested in other agro-ecological zones of Arid and semi-arid lands to confirm their tolerance stability.