# Identification and Characterization of Diaporthe citri as the Causal Agent of Melanose in Lemon in China

## TL;DR

This study confirms that the fungus Diaporthe citri causes melanose disease in lemons in China, providing new evidence through identification and pathogenicity tests.

## Contribution

The study provides the first comprehensive evidence linking Diaporthe citri to melanose disease in lemons in China.

## Key findings

- Diaporthe citri was consistently isolated from lemon fruits, leaves, and twigs with melanose symptoms.
- Pathogenicity tests confirmed that D. citri causes melanose symptoms on lemon fruits.
- Multigene phylogenetic analysis confirmed the identification of D. citri.

## Abstract

Lemon, widely used in food, medicine, cosmetics, and other industries, has considerable value as a commodity and horticultural product. Previous research has shown that the fungus Diaporthe citri infects several citrus species, including mandarin, lemon, sweet orange, pomelo, and grapefruit, in China. Although D. citri has been reported to cause melanose disease in lemons in China, key pathological evidence, such as Koch’s postulates fulfillment on lemon fruits and detailed morphological characterization, is still lacking. In May 2018, fruits, leaves, and twigs were observed to be infected with melanose disease in lemon orchards in Chongqing municipality in China. The symptoms appeared as small black discrete spots on the surface of fruits, leaves, and twigs without obvious prominent and convex pustules. D. citri was isolated consistently from symptomatic organs and identified provisionally based on the morphological characteristics. The identification was confirmed using sequencing and multigene phylogenetic analysis of ITS, TUB, TEF, HIS, and CAL regions. Pathogenicity tests were performed using a conidium suspension, and melanose symptoms similar to those observed in the field were reproduced. To our knowledge, this study provides the first comprehensive evidence for D. citri as a causal agent of melanose disease in lemons in China, including morphological characterization and pathogenicity assays on lemon fruits. This report broadens the spectrum of hosts of D. citri in China and provides useful information for the management of melanose in lemons.