Morphological and Molecular Characterization of Calonectria foliicola Associated with Leaf Blight on Rubber Tree (Hevea brasiliensis) in Thailand

Abstract

Leaf blight is commonly observed in rubber trees (Hevea brasiliensis) and can be caused by several fungal species. From October to December 2021, the emergence rubber tree disease was observed in Krabi province, southern Thailand. Small brown to dark brown spots developed on the leaves of rubber trees and later expanded into most parts of the leaves. Fungal isolates were isolated from infected tissues and a total of 15 Calonectria-like isolates were recovered from 10 infected leaf samples. Pathogenicity testing using the agar plug method revealed that four isolates caused leaf blight on rubber tree, similar to the situation in natural infections. Based on morphological study and the molecular properties of internal transcribed spacer (ITS), calmodulin (cal), translation elongation factor 1-α (tef1-α), and β-tubulin 2 (tub2) sequences, the four fungal isolates were identified as Calonectria foliicola. To the best of our knowledge, this is the first report of rubber trees pas a new host for C. foliicola in Thailand and elsewhere. This study reports on an emerging disease affecting rubber trees in Thailand, and the results are of benefit for the development of an appropriate method to manage this emerging disease in Thailand.

Morphological and Phylogenetic Evidences Reveal Lasiodiplodia chonburiensis and L. theobromae Associated with Leaf Blight in Hevea brasiliensis in Southern Thailand

“…In addition to the unidentified novel leaf disease, incidences of Phytophthora leaf fall disease caused by Phyotophthora citrophthora [10] and leaf fall caused by Neopestalotiopsis cubana and N. formicarium were also detected during this time frame in Thailand [4]. Lastly, another fungus that causes leaf fall in rubber trees, Calonectria foliicola, was also documented in the southern part of Thailand [9]. In addition, both fungal genera Neopestalotiopsis and Lasiodiplodia are species that can cause leaf disease in a wide variety of commercial plant species.…”

“…Healthy rubber leaves were surface disinfected using 70% ethanol. Inoculation was then performed using the agar plug method, as previously described by Thaochan et al [9]. Each fungal isolate was cultured on PDA and incubated at an ambient temperature for 3 days.…”

“…Increased fluctuations in extreme climate change have a major potential to lead to a higher pest risk and disease severity in rubber plantations [8]. Several reports showed that during 2019-2022 there was a prolonged monsoon season from September to January in southern Thailand [4,9]. During this period, there was an increase in overall fungal outbreaks on rubber plants and a novel leaf disease was also reported to appear during this time [4,9].…”

“…Several reports showed that during 2019-2022 there was a prolonged monsoon season from September to January in southern Thailand [4,9]. During this period, there was an increase in overall fungal outbreaks on rubber plants and a novel leaf disease was also reported to appear during this time [4,9]. Other factors favorable to a fungal disease outbreak were also reported, including a lower-than-average temperature (24-26 • C), higher rainfall averages (>100 mm), and a higher average relative humidity (>90% RH).…”

A New Species of Neoscytalidium hylocereum sp. nov. Causing Canker on Red-Fleshed Dragon Fruit (Hylocereus polyrhizus) in Southern Thailand

“…To determine which fungi isolated from the infected samples caused stem canker in H. polyrhizus , the candidate fungal pathogens were cultured on PDA for 5 days, and the agar plug method was conducted [ 17 , 18 , 19 ]. The stems of H. polyrhizus were wounded using sterile fine needles, and agar plugs (0.5 cm) cut from 5-day-old PDA culture plates of each fungal isolate were placed directly onto the wounded stems.…”