Studies on the leaf spot disease mulberry (Morus spp.)

Despite congenial climatic conditions the silk production in the State of Jammu and Kashmir has drastically declined from 76 tonnes in 1980 to 18 tonnes in 1991 (Anonymous, 1992). One of the factors responsible for the decrease in silk production was silkworm and mulberry disease. Almost all the commercial varieties of mulberry (Morus spp.) are prone to various diseases. The diseases not only reduce the leaf yield but impair its nutritional value. Feeding silkworms with diseased leaves adversely of mulberry is one among them. Studies were therefore, conducted to obtain some basic information of systematic nature of the disease so as to know its incidence, intensity symptomatology, causal fungus, perpetuation and management through cultural practices and fungicides. Survey conducted during 1999, revealed that the disease was prevalent in all the five districts of Kashmir Valley with maximum incidence (66.47%) and intensity (50.03%) in district Anantnag. The minimum disease incidence (17.17%) and intensity (7.91%) was observed in district Srinagar. However, an overall average incidence of 41% and intensity 24% of the disease was observed for the Kashmir Valley. The disease has exhibited symptoms very prominently on leaves and can be easily distinguished in five disease development stages. The disease initiates as cicular brown pin head sized spot, which gradually enlarges into dark brown spots surrounded by yellow zone, with whitish centre, producing conidia within acervulli. The mature spots coalesces into large lesions while passing through other stage of development and defoliates. The fungus was isolated and cultured on potato dextrose agar medium at 25 ±10C. its pathogenicity has been proved. The fungus produced hyaline, cylindrical, straight or curved, septate conidia with truncate base, guttulate cells within an acervullus. The average size of the conidia from culture and from fresh spots on leaves was found to be 47.4 x 4.16 and 45.97 x 3.5 µm, respectively. On the basis o symptomatology and morphological characters of the fungus causing leaf spot disease of mulberry, the causal fungus was identified as Phloeospora maculans (Bereng) Allesch an anamorph of Mycosphaerella mori (Fuckel) Wolf The mode of perpetuation of the fungus has been determined. The fungus perpetuates through winter in the form of dormant mycelium in diseased dead overwintered leaves. The conidial formation was observed during 2nd week of April on these leaves. The conidial production was highest, as recorded, (0.58 lac/cm2) on 8th May with 92.8% germination. No perfect state of the fungus was observed under existing conditions. A study on the effect of spacing and training height, revealed that with the increase in spacing and height there was gradual decrease in incidence and intensity of the disease. The maximum incidence (53.68%) and intensity (36.97%) was recorded at 90 x 45cm spacing and minimum incidence (36.21%) and intensity (23.39%) at 180 x 180 cm spacing. Whereas, in case of training the height, maximum incidence (56.46%) and intensity (33.70%) was recorded at height maintained at 10cm (Bush) and minimum incidence (38.835) and intensity (12.73%) at 150cm height (Tall). Screening of 34 mulberry genotypes during the year 1999 and 2000 revealed that none of the variety was immune to disease. Varieties like Obawase, KNG, Brantul and Senmestsu were categorised as resistant to the disease whereas, Botetul, Takawase and Sepentine were found highly susceptible. However, most of the commercial varities such as Goshoerami, Kokuso-20, 21 and 27 Kanva-2, Limoncina etc were found moderately susceptible. In an in vitro study, fungitoxicants both of systemic and protectant nature were significantly effective against conidial germination of Phloeospora maculans. Carbendazim @ 500 ppm inhibited 100 per cent conidial germination. Wheras, 100 per cent inhibition was obtained with triazoles at higher rate of 1000 ppm. Most of the protectants such as mancozeb, captan and zineb inhibited 100% spore germination when used @ 2000 ppm. whereas, similar effect was obtained with copper oxychloride when used @ 4000 ppm. Logistic Regression Model has been applied for the analysis of LD50 for various doses of fungitoxicants used against conidial germination. Under field conditions triazoles gave better results as compared to the carbendazim and protectant fungicides. Hexaconazole @ 500 ppm gave 88.45% disease control, whereas 81.35 and 78.60 per cent disease control was obtained with the application of carbendazim @ 500 ppm and captan @ 2000 ppm. Silk worms hybrid (NB4 D2 x SH6) were tested for the residual effect of fungitoxicants for their mortality, larval weight, cocoon weight and shell weight. The worms were fed in batches on the leaves sprayed 12 days, 8 days 4 days earlier to the feeding. The fungicides triazoles, carbendazim and captan did not show any adverse effect on the silkworms even they were fed leaves sprayed 4 days earlier to the feeding. Whereas, it was found to be safe with feeding of the leaves sprayed with zineb, mancozeb and copper oxychloride 12 days earlier