Phylogenetic, Morphological, and Pathogenic Characterization of Species Associated With Fruit Rot of Mandarin in California.

Alternaria rot caused by species is one of the major postharvest diseases of mandarin fruit in California. The aims of this study were to identify these species via phylogenetic analyses and morphological characteristics and test their pathogenicity on mandarin. Decayed mandarin fruits exhibiting Alternaria rot symptoms were collected from three citrus fruit packinghouses in the Central Valley of California. In total, 177 isolates were obtained from decayed fruit and preliminarily separated into three groups representing three species (, , and ) based on the colony characterization and sporulation patterns. To further identify these isolates, phylogenetic analysis was conducted based on DNA sequences of the second largest subunit of RNA polymerase II (), plasma membrane ATPase (), and Calmodulin gene regions in combination with morphological characters. Of the 177 isolates, 124 (70.1%) were identified as , and 53 (29.9%) were . The isolates initially identified as based on the morphological characteristics could not be separated from those of in phylogenetic analysis and thus considered . Pathogenicity tests showed that both species were pathogenic on mandarin fruit at both 5°C and 20°C. Our results indicated that two species, and , were responsible for Alternaria rot of mandarin fruit in California, with causing fruit rot on mandarin being reported for the first time.