Variation in pathogenicity of Colletotrichum graminicola (Cesati) Wilson and in symptom expression of anthracnose of Sorghum bicolor (L.) Moench

Abstract

Sorghum hybrids and varieties evaluated as resistant or susceptible following inoculation with a spore suspension of Celletotrichum graminicola, the anthracnose pathogen, had the same reaction when inoculated with toothpicks colonized with the fungus. Different dates of inoculation did not change the type of reaction. The anthracnose pathogen attacks all above ground plant parts ad it can elicit a variety of symptoms. The environment affects anthracnose expression on leaves, peduncles or panicles and only one type of symptom may be resent or predominant in a particular environment. At Experiment, Georgia, all three tissues were colonized but foliar anthracnose was more prevalent and severe. At two locations in Texas, foliar symptoms were rare and the least severe while panicle and peduncle anthracnose were common. In a field having overhead irrigation, symptoms developed in almost equal proportion in all three tissues. In Sete Lagoas, Brazil in all sorghum nurseries evaluated, foliar anthracnose was more frequent and severe than anthracnose on the peduncle or panicle. Similarly, sorghum plants sprayed in the greenhouse with a spore suspension of C. graminicola and placed in a humid environment, developed considerably more foliar anthracnose than plants with the same procedure but not placed in a humid environment. Previously undescribed external colonization of sorghum kernels by C. graminicola was observed in Guatemala, Brazil, Georgia and Texas. Clusters of acervuli occurred as minute, black structures, growing superficially on the pericarp in concentric rings around the stylar area. Kernel colonization was observed on anthracnose resistant and susceptible sorghum plants growing both in the field and in the greenhouse. It appeared that colonization occurred very rapidly on mature kernels under moist or rainy conditions. Kernel colonization, in many cases, reduced grain quality by decreasing seed germination, seed emergence and 100-kernel weight. Seedlings from kernels with extensive external colonization planted in the greenhouse had abundant acervuli of C. graminicola on the coleoptile and foliar anthracnose symptoms, demonstrating the possibility of seed transmission of C. graminicola...