Disease incidence, lesion size, and sporulation in Colletotrichum truncatum as influenced by lentil genotype and temperature

The development of anthracnose [Colletotrichum truncatum] was studied at fo ur temperatures (16:12, 20:16, 24:20, and 28:24 degrees C, day:night) on fi ve partially resistant lentil (Lens culinaris) genotypes (PI 299331, PI 320 937, PI 345629, 458-57, and cv. Indianhead) and the susceptible cv. Eston, using a single pathogen isolate. Disease incidence was 100% across the temp erature range in the susceptible cultivar, but varied between 33 and 100% a mong the resistant genotypes. The increase in disease incidence with temper ature was linear, but was affected by the level of host resistance. For eac h genotype, lesion size increased with increasing temperature. Maximum lesi on size was reached at 24:20 degrees C and sharply decreased at 28:24 degre es C. Percent sporulating stem lesions also increased with temperature, but at each temperature the highest sporulation occurred on cv. Eston, consist ently remained lowest on PI 320937, and was intermediate in the other genot ypes. The results showed that both temperature and genotype significantly a ffected disease incidence, lesion size, and sporulation and that the optima l temperature for anthracnose development occurred with day time temperatur es of 20-24 degrees C, regardless of level of host resistance.