First Report of Rhizoctonia solani AG-4 HG-I Causing Fruit Rot on Tomato in Mexico.

Abstract

The culture of tomato (Solanum lycopersicum L.) is an important food, fruits are source of vitamins and minerals, they also prevent chronic diseases such as cancer and vascular diseases (Willcox, 2003); in Mexico 47,372 ha are destined to tomato cultivation (SIAP, 2019). In February 2021, in a tomato plantation located in Rancho el Progreso (17.743639N, 99.243250W, 1554 masl), municipality of Zitlala, Guerrero, Mexico, the presence of rot of tomato fruits hybrid DRD-8551 (seed company, Seminis) was detected in tomatoes grown in greenhouses. Disease incidence was 8% in a sample of 250 plants. The infected fruits initially exhibited circular to irregular lesions, with a soft rot of infected tissue, which in advanced stages infected more than 50% of the fruit surface and a white to light brown mycelium cover was observed. It was observed that fruits were those that were closer to the soil were heavily affected. From infected fruits, cuts of approximately 0.5 cm were made, disinfested with 1% NaOCl and transferred to PDA medium, using this technique for all samples that were processed. Eight representative isolates were purified; developed colonies were initially light-white, after seven days they turned light brown. Right-angle hyphae were observed, with a slight constriction at the base of the branches, and produced dark brown sclerotia; morphological characteristics were consistent with those described for Rhizoctonia solani Kühn (Parmeter 1970). To confirm the anastomosis group (AG), the ITS region was amplified with the ITS1 and ITS4 primers (White et al. 1990) from the ESCJZ9 and ESCJZ10 strains. A search with BLAST tool indicated that both strains were 99.4% identity with R. solani AG-4 HG-I strain ICMP 20043 (GenBank: KM013470) (Ireland et al. 2015). Phylogenetic analysis compared with different sequences of AGs, allowed to group ESCJZ9 and ESCJZ10 strains with the clade AG-4 HG-I. The sequences were deposited in GenBank (MZ274468 for ESCJZ9 and, MZ274469 for ESCJZ10). Pathogenicity was confirmed by inoculating 15 healthy tomato fruits (hybrid DRD-8551), in which a portion of mycelium from the ESCJZ9 strain was inserted with a sterile toothpick in two points / fruit. In eight fruits only a sterile toothpick (two points / fruit) was inserted. The fruits were housed in laboratory conditions at average temperature of 27 °C. After five days, fruit rot symptoms were observed in all inoculated fruits, similar to those observed in the field. Control fruits remained asymptomatic. Additional pathogenicity tests were performed on 50 tomato plants (hybrid DRD-8551) of 15-day-old. Two 5 mm diameter mycelial discs from strain ESCJZ9 were deposited at the base of the stem 10 mm below the soil surface. As control treatments, sterile PDA was deposited in 20 plants. The plants were housed in a greenhouse at an average temperature and relative humidity of 28 ° C and 85%, respectively. After four days, all the inoculated plants showed root and stem rot and leaf flaccidity. Control plants remained asymptomatic. R. solani was re-isolated from the infected fruits and plants, fulfilling Koch's postulates. Previously, in Iran and Brasil R. solani AG-4 HG-I has been reported that caused stem and fruit rot on tomato (Rahimian 1988; Kuramae et al. 2003). In Mexico R. solani AG-4 has been reported in other solanaceae species such as potato and chili (Virgen-Calleros et al. 2000; Montero-Tavera et al. 2013). To our knowledge, this is the first report of R. solani AG-4 HG-I causing tomato fruit rot in Mexico. This research provides information in order to establish disease management strategies. It is important to establish measures to minimize the spread of this pathogen to other tomato-producing areas of this country.