Variability of Colletotrichum isolates inciting anthracnose in mango (Mangifera indica L.)
Loading...
Files
Date
2016
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Department of Plant Pathology, College of Horticulture, Vellanikkara
Abstract
The present investigation on “Variability of Colletotrichum isolates inciting anthracnose in mango (Mangifera indica L.)” was carried out in Department of Plant Pathology, College of Horticulture, Vellanikkara during 2014-2016 to elucidate the variability existing in Colletotrichum causing
anthracnose of mango in terms of pathogenicity, phenotypic characters,
compatibility of isolates and their sensitivity to plant protection chemicals.For the isolation of pathogen, purposive sampling surveys were conducted at different locations of Thrissur and Palakkad districts. Disease samples were collected from seven selected varieties of mango viz. Muvandan, Neelum, Prior,
Banganapalli, Alphonso, Chandrakaran and Sindhooram. Totally 30 isolates were
obtained of which, six isolates were from Muvandan, eight from Neelum, four each from Prior, Banganapalli and Alphonso, one from Chandrakaran and three from Sindhooram. Pathogenicity of all the thirty isolates was proved on their respective host and observed symptom development in two to three days.
Symptomatology of anthracnose disease of mango was studied in detail
under natural and artificial conditions. Under natural condition, various types of symptoms like small black spots with shot hole, large spots with black margin, infection on leaf margin, lesions with or without halo and distortion of large area
were observed on leaves of different varieties. Twig infection with dieback
symptom was observed on all varieties. On the fruits of Muvandan and Neelum, black sunken spots and tear stain symptoms were noticed. All these typical symptoms were not observed under artificial inoculation and in general, all the 30
isolates produced light brown to black irregular lesions on their respective varieties. Phenotypic characters of the 30 isolates were studied on Potato Dextrose Agar (PDA) and Green Bean Agar (GBA) media. Variations in the cultural characters like colony texture, shape, spore formation, development of acervulus and pink spore mass formation were recorded on both media. Among the 30 isolates, only 11 isolates showed the development of acervulus of which, only nine isolates produced pink spore mass on PDA medium. Variation in cultural characters was not observed on GBA medium and the isolates did not produce fruiting body on this medium. But early spore formation was recorded by all the
isolates on this medium. Growth rate of each isolate on PDA and GBA media was calculated and based on which the isolates were grouped as fast growing (Group I) and slow growing (Group II). The isolates PI, BL2, BL3 and AL4 were
recorded as fast growing isolates on both media.
Morphological characters of hyphae, spores, and setae of the isolates showed variation. The average size of conidia was recorded in the range of 13.52- 16.99 x 3.40-5.16 μm. Acervulus development was observed in 11 isolates on PDA medium, but acervulus with setae was noticed only in six isolates viz.,
MT1, NT1, BL1, AL1, CT and SL1. The size of setae was recorded in the range
of 86.32-142.30 x2.08-4.75 μm. Cluster analysis of all 30 isolates was done based on the cultural and morphological characters. Maximum variation was recorded at 10 per cent similarity level, where 30 isolates were grouped into two major
clusters viz. A1 and A2 accommodating three and 27 isolates respectively. Screening for vegetative compatible combinations of the isolates was studied using dual culture technique. Out of the 465 combinations, only 76 showed compatible reaction of intermingling of hyphae, while others showed incompatible reactions. The isolates BL2 recorded the highest compatible
conditions (8 nos.) with other isolates. To study the variations in the pathogenic
efficiency, the isolates were cross inoculated on other varieties. The results showed variations in the time taken for symptom development, spot size on five days after inoculation and number of varieties infected by the isolates. The isolate, CT recorded infection on all seven varieties followed by NF3 and PL1 recorded infection on six varieties. Based on the efficiency of each isolate to infect number of varieties and time taken to symptom expression, these 30 isolates were grouped into three as highly virulent (HV), moderately virulent (MV) and less virulent (LV) isolates. Accordingly NF3, PL1 and CT were
grouped as highly virulent isolates. On the basis of phenotypic and pathogenic characters, seven virulent isolates of C. gloeosporioides, one from each variety were sent to National Centre for Fungal Taxonomy (NCFT), New Delhi and the identity of these isolates was confirmed as Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. by NCFT with ID No. 8214.16-8220.16. In vitro evaluation of plant protection chemicals (three contact fungicides, four systemic fungicides and two insecticides) was carried out to check the sensitivity of isolates. All the four systemic fungicides showed cent per cent inhibition on the growth of 30 isolates and were found most effective for the control of C. gloeosporioides. Bordeaux mixture (1 %) and copper hydroxide (0.15%) recorded cent per cent inhibition on the growth of 28 and 24 isolates respectively. The insecticides, malathion (0.1 %) and dimethoate (0.05%) also recorded inhibition of fungal growth in the range of 50.74 to 83.70 per cent. The results of the present study proved the existence of considerable phenotypic and pathogenic variability among the 30 isolates of C. gloeosporioides obtained from seven mango varieties grown in Kerala. This information could establish a base for the future investigation on the mechanism of genetic variability of the pathogen.
Description
PG
Keywords
null