Differential Susceptibility of Tree Tomato (Solanum betaceum) Cultivars to Late Blight Caused by Phytophthora betacei

Host-pathogen interactions of a new species of Phytophthora, causal agent of late blight of tree tomato (Solanum betaceum Cav.), identified as Phytophthora betacei, were investigated with four different cultivars. Thirty-six P. betacei isolates, collected from southern Colombia between 2008 and 2009, were used to inoculate common tree tomato cultivars, Comun, Hibrido, Injerto, and Holandes. Data on incubation and latent periods as well as infection efficiency, lesion development, and total sporulation were collected via detached leaf assays. Significant differences in susceptibility, based on the parameters measured, were observed. Comun was the most susceptible cultivar, followed by Injerto, Hibrido, and Holandes. The mean incubation period was lowest for Comun at 125.6 h post-inoculation (hpi) and highest for Hibrido at 139.4 hpi. No significant differences in latent period were observed. All 36 isolates produced necrotic lesions on Comun, and 33, 24, and 21 caused infection on Injerto, Hibrido, and Holandes, respectively. Two isolates were able to cause infection only on Comun, and 13 isolates were able to infect all four cultivars. Infection efficiency was significantly higher for the cultivar Comun, followed by Injerto, Hibrido, and Holandes. Average lesion size was larger on Comun than on any other cultivar. An inverse relationship of lesion size and total sporulation was observed. Comun had significantly lower total sporulation than Hibrido and Holandes, which had the smallest average lesion sizes. These data show variation in pathogenicity of P. betacei isolates, under controlled conditions, and differential susceptibility of four distinct S. betaceum cultivars.