3.4.47
PHYTOTOXINS AS A RAPID AND USEFUL SOURCE FOR SELECTION OF DISEASE RESISTANCE IN CHICKPEA

SS ALAM1, IA KHAN1, M ANSAR2 MI CHOUDHRY3 and A REHMAN3

1Nuclear Institute for Agriculture and Biology, PO Box 128, Faisalabad, Pakistan; 2Plant Pathology Section, Ayub Agriculture Research Institute, Jhang Road, Faisalabad, Pakistan; 3HEJ Research Institute of Chemistry, University of Karachi, Karachi 75270, Pakistan

Background and objectives
Chickpea (Cicer arietinum) is an important grain legume crop containing cheap source of protein for the poor inhabitants of the developing countries. Ascochyta blight (Ascochyta rabiei), wilt (Fusarium oxysporum f.sp ciceris), and phytophthora blight (Phytophthora megasperma) are among the major diseases of chickpea. Epiphytotics of the ascochyta blight have resulted in almost total loss of the crop. These fungi were identified to produce phytotoxins that are involved in their diseases. The aim of this work was to use phytotoxins for selection of disease resistant materials in chickpea.

Materials and methods
The phytotoxins solanapyrone A and C were isolated and purified from culture filtrate of A. rabiei [1]. Cell suspensions of different chickpea cultivars were added to two-fold dilution of toxin preparations in the wells of microtest plates. After incubation for 3 h at 25C the vital stain fluorescein diacetate was added and the live and dead cells were counted under an inverted microscope with epifluorescence optics. The LD50 values were extracted from graphs of probit percent cell death (corrected for control values) plotted against log2 dilution factor. Culture filtrates of F. oxysporum f.sp. ciceris and P. megasperma were obtained by growing these fungi for 21 days at 25C [2]. Twenty day-old seedlings of chickpea were tested against toxin preparation of A. rabiei and culture filtrates of the other two fungi.

Results and conclusions
Isolated cells of chickpea ILC 3279, CM-88, CM-72, ILLC-195 were less sensitive to solanapyrone A and C and were resistant/tolerant to pathogens in their field screening. Cultivars sensitive to phytotoxins were also susceptible to ascochyta blight. Cultivars sensitive to culture filtrates of F. oxysporum f.sp. ciceris and P. megasperma were also susceptible to these pathogens in field experiments. Fifteen lines identified insensitive to culture filtrate were found resistant to phytophthora blight. CM-88, which was insensitive to phytotoxins of A. rabiei and to culture filtrate of F. oxysporum f.sp. ciceris, was released for commercial cultivation as a new variety, resistant to blight and wilt diseases of chickpea. A novel phytotoxin was isolated from culture filtrate of F. oxysporum f.sp. ciceris involved in the wilt disease. The mass spectrometry of the active compound revealed the molecular formula C16H16O5. Selection of insensitive plants against these phytotoxins was found to be a most rapid, economical and useful method of identification for disease resistant materials in chickpea.

References
1. Alam SS, Bilton JN, Slawin AMZ, William DJ, Sheppard RN, Strange RN, 1989. Phytochemistry 28, 2627-30.
2. Alam SS, Khan IA, 1996. Pak. J. Phytopathology 8, 132-135.