Identification and Pathogenicity of Fungal Pathogens Associated with Stem-End Rot of Avocado in California

Abstract

Stem-end rot of harvested avocado fruit commonly occurs wherever the crop is cultivated. Multiple fungal species have been described as causal agents. To determine the causal pathogens of stem-end rot in California, fungal isolations were conducted from symptomatic fruit, and fungi were identified by morphological and molecular techniques. In 2010 and 2011, a total of 177 isolates were recovered from 290 avocado fruit collected from seven orchards in one of the major avocado growing areas in Southern California. The majority of isolates was identified as Neofusicoccum luteum (65%), with the remainder either as Colletotrichum gloeosporioides (33%) or Phomopsis sp. (2%). In a pathogenicity test, N. luteum caused significantly (P < 0.05) more severe stem-end rot than either C. gloeosporioides or Phomopsis sp. No significant (P > 0.05) differences in stem-end rot severity were observed between inoculations with N. luteum isolated from fruit stem-end rot and N. luteum or N. parvum isolated from branch cankers. This confirms that stem-end rot of avocado can be initiated by fungi causing branch cankers. Although low humidity and rainfall during much of the growing and harvest seasons in California are considered unfavorable conditions for the development of avocado stem-end rot, the identification of the causal pathogens is of value when decays have to be managed during outbreaks, and it stresses the importance of managing branch cankers.

Characterisation and pathogenicity of fungal species associated with branch cankers and stem-end rot of avocado in Italy

“…were less virulent in our inoculation studies compared to N. parvum. The Diaporthe spp., were isolated exclusively from branch cankers, but are reported to cause avocado fruits disease elsewhere (Twizeyimana et al 2013). In this study, when Diaporthe spp.…”

“…This fungus was recovered from all orchards sampled and was identified by comparing morphology and through phylogenetic analysis (Phillips et al 2013). Neofusicoccum parvum is reported to be a major stem canker and stem-end rot pathogen of avocado in California, Australia, New Zealand and South Africa (Darvas et al 1987;Hartill and Everett 2002;McDonald et al 2009;Twizeyimana et al 2013 (Ismail et al 2013, Phillips et al 2013. Indeed, this is the first report of N. parvum causing disease on avocado (branch canker and stem-end rot) in Italy.…”

“…In California, New Zealand and South Africa the imperfect stage, Phomopsis spp. have been reported as pathogens of minor importance on avocado in both pre-and postharvest situations (Hartill and Everett 2002;Eskalen et al 2013;Twizeyimana et al 2013). Considering that several Diaporthe spp.…”

“…(Hartill and Everett 2002;Valencia et al 2011). Recently, Twizeyimana et al (2013) showed that the pathogens causing cankers may be a source of inoculum for stem-end rot. Conversely, fungal species associated with stem-end rot could cause branch cankers (Hartill and Everett 2002;Menge and Ploetz 2003).…”

Phyllospheric Microbiomes: Diversity, Ecological Significance, and Biotechnological Applications

“…and Fagus crenata B1 (Osono 2006), Colletotrichum gloeosporioides and Phomopsis sp. (Rivera-Vargas et al 2006;Twizeyimana et al 2013), and Table 5.1 listed some examples of phyllosphere fungal endophytes. Osono (2008) reported that endophytic Colletotrichum gloeosporioides and C. acutatum, and epiphytes Pestalotiopsis sp., Aureobasidium pullulans, Phoma sp., and Ramichloridium sp.…”