Stalk rot fungi affect grain sorghum yield components in an inoculation stage-specific manner

Although stalk rots are among the most prevalent and destructive diseases of sorghum, no systematic crop loss assessment has been reported for these diseases under controlled-inoculations. The objective of this study was to assess the impacts of Fusarium stalk rot and charcoal rot on grain sorghum yield components when plants were inoculated at two growth stages (GS). Four genotypes were field evaluated against three Fusarium spp. (F. thapsinum, F. proliferatum, F. andiyazi) and Macrophomina phaseolina. Inoculations were performed at GS1 (30 d after emergence) and GS3 (14 d after flowering). Panicles were harvested at physiological maturity and assessed for total seed weight (TSW), 100-seed weight (100-SW), and total seeds per panicle (TSP). The total number of reproductive sites and unfilled spikelets were counted per rachis (TRSR and NUSR, respectively) and panicle (TRSP, NUSP) bases. Length and nodes crossed by the lesion in split stems were measured to evaluate disease severity. Pathogens significantly reduced TSW in comparison to the control at both GS1 and GS3. The four pathogens, on average, caused greater TSW reductions when inoculated at GS1 (52%) than at GS3 (37%). All pathogens reduced TSP upon GS1 inoculation and 100-SW upon GS3 inoculations. All pathogens significantly reduced seed set percentage when plants were inoculated at GS1 while inoculations at GS3 did not have a significant impact. GS1 inoculations significantly decreased TRSP, demonstrating pathogen interference with head formation resulting in smaller heads than control. Although inoculations at GS1 had a greater impact on yield, inoculations at GS1 and GS3 did not significantly differ in disease severity. This study revealed inoculation stage-specific effects of stalk rot pathogens on yield parameters and provided insights into key yield traits to be emphasized in sorghum breeding programs to produce stalk rot tolerant sorghum genotypes.