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Sorghum anthracnose caused by Colletotrichum sublineolum is one of the most destructive diseases affecting sorghum production in Ethiopia. Pathogenic variability of C. sublineolum isolates on some sorghum differentials under greenhouse condition was evaluated in Jimma, Ethiopia. Highly significant (P < 0.001) differences among sorghum differentials, C. sublineolum isolates and their interactions on incubation period, aggressiveness, virulence index, virulence, the first and final anthracnose severity assessments, disease infection rate and AUDPC were studied. Among the interactions, the interaction between CsAs7 (isolate from Assosa zone field 7) and sorghum differentials had the shortest mean incubation period (3.5 days), highest first and final anthracnose severity, highest virulence index, fastest disease infection rate and highest AUDPC as compared to others. This isolate showed the most aggressive and virulent reaction than others followed by CsJm5. The interaction of PI570726 and SC748-5 sorghum differentials and all C. sublineolum isolates produce 100 and 80% resistant reactions, respectively and they could be used as good sources of resistance genes for breeding programs for sorghum anthracnose management. [ABSTRACT FROM AUTHOR]

Diseases cause enormous losses of yield and quality for crop producers worldwide. To meet future food demands, crops are bred for resistance to as many of these maladies as possible. One such disease, anthracnose [Colletotrichum sublineola], is a fungal disease of great importance to sorghum [Sorghum bicolor, L. Moench] production because it causes significant annual economic losses in the crop. Breeding for anthracnose resistance requires time-consuming phenotyping, which is subjective and conditional to the evaluator. It is possible that quantitative assessment using high-throughput methodologies to estimate the trait may be more effective. In this study, we present an in-depth statistical analysis of fixed-wing, unmanned aerial system (UAS) evaluation of anthracnose incidence and severity in sorghum using normalized difference vegetation index (NDVI). In early phases of infection, correlations between ground-truth and UAS estimates of anthracnose were moderate but they increased substantially by the end of the season (r = −0.55 to −0.95). Additionally, both metrics had moderate-to-high repeatabilities throughout the growth period (R = 0.60-0.90), indicating they were consistently able to differentiate genotypes. Finally, we found that the UAS-derived measurements (R2 = 0.377, 0.473) were better associated with ground-truth measurements (R2 = 0.278, 0.347) for grain yield under anthracnose pressure. The results of this study indicated that fixed-wing UAS could potentially be effective for evaluating anthracnose disease present in sorghum, and the greater range of the UAS allowed the effective evaluation of larger numbers of plants than ground truth or traditional remote sensing methods. [ABSTRACT FROM AUTHOR]

Seven inoculation methods were tested at multiple field sites with different climates in Texas and Mexico to determine the technique most suitable for routine screening of sorghum (Sorghum bicolor (L.) Moench) germplasm for resistance to Claviceps africana (causal agent of sorghum ergot). A single spray or sponge inoculation before flower initiation followed by bagging of the panicles for seven days was the most reliable technique for identifying ergot-resistant sorghum genotypes. This method ensures that unfertilized ovules and infection sites were exposed to the pathogen at the time of greatest vulnerability, thereby reducing the influence of flowering characteristics. This method is repeatable and rapid, thus providing a useful procedure for germplasm evaluation. Disease symptoms on sorghum genotypes are expressed within a reasonably short period. Compared with the other methods, inoculated and bagged panicles resulted in a significantly higher percentage of ergot-infected florets in all environments. Across sorghum lines, no significant increases in ergot severity were observed between inoculated nonbagged, inoculated and misted, and water-sprayed control panicles. In all environments, percent ergot severity per panicle across treatments generally increased from 10 to 15 days after inoculation with negligible increases in disease severity after 15 days. This suggests that ergot assessments after inoculation can be concluded within 15 days. None of the genotypes tested was completely resistant to sorghum ergot. However, NC+8R18, NC+7W97, and the two sister-lines of IS8525 (IS8525J and IS8525D) exhibited more resistance to ergot than the other sorghum lines tested. [ABSTRACT FROM PUBLISHER]

Grain mold, caused by several species of fungi, reduces grain yield and quality. This study examined the effect of the two most common grain mold fungi, Fusarium thapsinum and Curvularia lunata, inoculated singly and together on germination and seed mycoflora. Germination rates for the different cultivars have been reported in details previously. C. lunata was the most frequently isolated fungal species followed by F. thapsinum and F. semitectum. Non-inoculated control samples had Alternaria spp. and F. semitectum as themost frequently recovered fungal species followed by C. lunata. There were highly significant negative correlations between germination and C. lunata (r =-0.44 and P < 0.01) in 2000 and between germination and F. thapsinum (r = -0.52 and P < 0.01) in 2001. Significant negative correlations between F. semitectum and F. thapsinum, and highly significant negative correlations between F. thapsinum and C. lunata were observed. Data from this study indicate that the fungal species present, the environment, and the sorghum cultivar all influence seed mycoflora. [ABSTRACT FROM PUBLISHER]

The potential of corn earworm moths Helicoverpa zea, an important pest of sorghum in Texas, as a passive vector of sorghum ergot, Claviceps africana was assessed. Laboratory-reared (females and males) and field-moths trapped in sex pheromone traps were confined in screen cages with potted male-sterile sorghum line AT×623 that had been artificially infected with sorghum ergot and was producing massive amounts of honeydew that contained spores of the fungus. In the cages, moths were observed feeding on the honeydew. When laboratory-reared moths contaminated with C. africana spores were released for 12 or 48 h in cages containing healthy greenhouse- or field-grown male-sterile sorghum plants at anthesis, the levels of ergot severities on the panicles ranged from 0.5-90%, per panicle. The levels of ergot infection on greenhouse- and field-grown AT×623 exposed to ergot contaminated fieldtrapped males for 48 h ranged from 0-81.7%. Mean external contamination of laboratory-reared and field-trapped moths placed in a soapy wash was 1.4 × 10[sup 5] and 4.7 × 10[sup 4] conidia/ml, respectively. This study demonstrated that contaminated adult corn earworm could transmit the sorghum ergot from diseased to healthy panicles when environmental conditions are favorable for infection. Thus, migrating moths and other highly mobile pest species have the potential to transport C. africana over relatively large distances. [ABSTRACT FROM AUTHOR]