Variability of aggressiveness and virulence of Phytophthora palmivora influencing the severity of papaya fruit rot in postharvest in Bahia, Brazil

Abstract

Papaya (Carica papaya L.) is susceptible to various production diseases, therefore, studies are needed to reduce them. Papaya fruit rot (Phytophthora palmivora (Butler) Butler) is one of the fungal diseases present in producing regions (Bahia and Espírito Santo) of Brazil. This study aimed to evaluate the variability of aggressiveness and virulence of Phytophthora palmivora that influence the severity of fruit rot in postharvest in vitro and in vivo. The following mycelial growth characteristics were evaluated: (a) mycelial growth speed index (MGSI); (b) mycelial growth speed potential (%MGSI); (c) spore production (SP); (d) spore production potential (%SP) and (e) growth potential (%GP) of 21 strains. The maximum mycelial growth after 120 hours of cultivation in strains of P. palmivora ranged between 27 and 81 mm for strains 355 and 356, respectively. Strains 356, 363, 839, 1056, 1060 and 1189 showed the highest MGSI values. These strains have a high colonization speed and, therefore, good capacity to settle on the substrate. Among them, strains 356, 1060, 839 and 363 showed better %MGSI when compared with the other strains. The most virulent were: 356, 357, 358, 359, 361, 363, 839, 1055, 1056, 1057, 1060 and 1189, whereas the most aggressive were 356 and 1060.

Additional keywords: mycelial growth; spore production; fungal rot.