THE RELATIONSHIP BETWEEN MATURITY OR SENESCENCE OF TOBACCO LEAVES AND BROWN SPOT

Zhang Minghou Zhang Jingrong Jia Wenxiang Zhao Ying Ma Rui (Northeast Agricultural University, Harbin 150030)

Tobacco brown spot Maturity or senescence Susceptibility Alternaria alternata

The results of inoculating 1-7 lower leaves of tobacco pot plants of five cultivars showed:as leaves became mature or senescent from bottom upward to top of tobacco plant,their color was changed from green to yellow,the chlorophyll content was decreased,dissolvable sugar content of leaf sap and reducing sugar of diffused leaf sap were increased,but the disease resistance was decreased correspondingly.If leaf color was used as creterion of resistance,green growing leaf was immune;rather yellowish green leaf was highly resistance,only pin tip size brown specks were formed which could neither expand nor sporulate;greenish yellow leaf was moderately susceptible,spots about 0.2 cm in diameter could be formed on it,and most of them could no enlarge any more under general climate condition;mature yellow leaf was high.Susceptible,on which typical spots larger than 0.5 cm in diameter were always formed and sporulated profusely.Spore germination rate and disease index after inoculation with medium of 1% glucose were higher than with medium of 1% sucrose.Spore germination rate and disease. incidence after inoculation with medium of mature tobacco leaf were also higher than medium with yellowish green and green tobacco leaves.The results indicated that maturity of tobacco leaf was highly correlated with the resisatance to brown spot disease.