Aetiology and molecular characterization of the pathogens associated with soft rot disease of Aloe vera (L.) Burm. f.

Abstract

Soft rot is a devastating disease of aloe and the infected plants developed symptoms of rotting tissues from collar region upwards. Aloe plants artificially inoculated with a Dickeya spp. (reported earlier as the causal agent) at the root zone but did not develop the disease symptoms, eliminating the possibility of pathogen to entering through roots. Besides, a Fusarium spp. was repeatedly isolated from collar regions of the naturally infected plants. Further, it was established that lesions produced due to fungal infection predisposed the subsequent infection of the bacterial pathogen. Sequencing results and phylogenetic analysis based on three partial genes of bacteria (dnaX, icdA and mdh) and fungus (ITS, TEF-1α and RPB-2) confirmed the identity of pathogens as Dickeya zeae and Fusarium falciforme, respectively. An artificial inoculation technique was developed for quick screening of aloe germplasm for resistance of bacterium. Among 40 accessions screened, none was found resistant, however, F. falciforme failed to produce lesion on two accessions (Guj4 and Raj3), consequently making them resistant to soft rot disease upon combined inoculation with both the pathogens. Besides the genetic constituent, rapid rotting was observed at 35 °C but not at and below the 15 °C temperature. In planta, the bacterium concentration increased gradually with the rise of incubation temperature between 15 and 35 °C. The present study suggests possible management aspects of the problem through (i) exploiting host resistance and (ii) escaping post–harvest decay by storing and transporting aloe leaves at temperatures ≤ 15 °C and (iii) avoidance of water stagnation in field.