Occurrence of Anthracnose Caused by Colletotrichum truncatum on Chickpea (Cicer arietinum) in Malaysia

Abstract

At least nine Colletotrichum species, particularly Colletotrichum truncatum, have been recorded on legumes worldwide (1). In June 2010, samples of chickpea leaflets showing leaf spot disease symptoms were collected from experimental farms in Ladang Dua, Selangor state of Malaysia. Tan lesions with darker brown borders were observed on leaflets and were associated with premature leaf drop. Stem lesions initially appeared on the lower parts of stems and later progressed higher in the plant. Lesions often girdled the stem and caused severe dieback. Abundant acervuli developed in the lesions visible as black dots. Foliar lesions were removed, surface sterilized in 1% sodium hypochlorite for 2 min, rinsed twice with distilled water, dried on sterilized tissue paper, plated on PDA plates, and incubated at 25°C (3). Three isolates of the fungus were obtained and identified as C. truncatum on the basis of morphological characteristics (2). The isolates were deposited in the University Putra of Malaysia Culture Collection (UPMCC). Colony characteristics on PDA varied from greyish white to dark in color and exhibited mycelial growth with sparse acervuli. The isolates produced both sclerotia and setae in culture. Conidia (mean ± SD = 22 ± 0.83 × 3.6 ± 0.08 μm, L/W ratio = 6.1) produced in acervuli were falcate, hyaline, and aseptate, with tapering towards the acute and greatly curved apex. The conidial mass color varied from pale buff to saffron. Isolates produced simple to slightly lobed, mainly short clavate appressoria (mean ± SD = 9.60 ± 0.36 × 6.67 ± 0.29 μm, L/W ratio = 1.45). Amplification and sequence analysis of coding and none-coding regions of the ITS-rDNA (GenBank Accession JX971160), actin (JX975392), β-tubulin (KC109495), histone (KC109535), chitin synthase (KC109575), and glyceraldehyde-3-phosphate dehydrogenase (KC109615) obtained from the representative isolate, CTM37, aligned with deposited sequences from GenBank and revealed 99 to 100% sequence identity with C. truncatum strains (AJ301945, KC110827, GQ849442, GU228081, GU228359, and HM131501 from GenBank). Isolate CTM37 was used to test pathogenicity in the greenhouse. Five chickpea seeds of cultivar ILC-1929 were sown per pot in four replications. Ten days after seedling emergence, plants were inoculated with a spore suspension (concentration = 106 conidia ml-1) and check pots were sprayed with distilled water. After inoculation, the plants were covered with plastic bags for 48 h and kept at 28 to 33°C and >90% RH. After incubation, the plastic bags were removed and the plants were placed on greenhouse benches and monitored daily for symptom development (3). One week after inoculation, typical anthracnose symptoms developed on the leaves and stems of inoculated plants including acervuli formation, but not on the checks. A fungus with the same colony and conidial morphology as CTM37 was recovered from the lesions on the inoculated plants. The experiment was repeated twice. The ability to accurately diagnose Colletotrichum species is vital for the implementation of effective disease control and quarantine measures. We believe this is the first report of C. truncatum causing anthracnose on chickpea in Malaysia.