Resistance Of Litchi Anthracnose Pathogen Colletotrichum Gloeosporioides Penz. To Thiophanate-methyl,prochloraz,and Azoxystrobin

Litchi anthracnose?Colletotrichum gloeosporioides Penz.?is one of the most significant diseases of litchi,which can cause economic damage to litchi before and after harvest.At present,chemica l control is the main measure which widely used for controling litchi anthracnose.Thiophanate-methyl,prochloraz and azoxystrobin have been used to control litchi Anthracnose for many years,but there is no report on the resistance or fail prevention.In this study,356 isolates of C.gloeosporioides from Guangdong,Fujian,Hainan,Jiangxi,Guangxi,Sichuan and Yunnan provinces were collected from 2012 to 2016.The sensitivities of these isolates were determined,to the fungicides thiophanate-methyl,prochloraz and azoxystrobin,respectively.The baseline sensitivity of C.gloeosporioides to thiophanate-methyl,prochloraz and azoxystrobin was determined according to their 50% effective concentration(EC₅₀)value.And the resistance of isolates was monitored according to FAO method.At the same time,the biological characteristics,cross resistance and molecular mechanism of the resistant isolates?or mutants?were studied.The main results were as follows:The sensitivies of 351 isolates of C.gloeosporioides to thiophanate-methyl were determined by mycelium growth rate method,which suggests that the baseline sensitivity ranged from 0.2529 to 1.3950 ?g/m L with a mean of?0.6433±0.2156??g/m L.Based on the baseline sensitivity,the resistance index of each C.gloeosporioides to thiophanate-methyl was calculated.The results showed that there were 202 sensitive isolates,1 low resistant isolate,9 moderate resistant isolates and 139 high resistant isolates.The number of resistant isolates reached 149,accounting for 42.45% of the total population.The adaptability of resistant isolates to thiophanate-methy was not significantly different from that of sensitive strains due to the resistant isolates had no significant differences in biological characteristics.The resistant mechanism of C.gloeosporioides to thiophanate-methyl was mainly due to the mutation of amino acid at position 198 of ?-tubulin gene.The sensitivity of a population with 356 isolates of C.gloeosporioides to prochlorazines were determined by mycelium growth rate method,which suggests that the baseline sensitivity ranged from 0.0147 to 0.1867 ?g/m L with a mean of?0.0573 ± 0.0299??g/m L.Based on the baseline sensitivity,the resistance index of each C.gloeosporioides to prochlorazines was calculated and 1 resistance isolate was found.The sensitivity distribution showed that a few strains had abnormal distribution.Compared with wild-type parent isolates,the resistant isolates significantly decreased on the mycelia growth,dry weight of mycelial,sporulation,germination and pathogenicity.The sensitivies of 174 isolates of C.gloeosporioides to azoxystrobin were determined by spore germination method,which suggests that the baseline sensitivity ranged from 0.0026 to 225.1941 ?g/m L with a mean of?11.8871 ± 33.4922??g/m L.Based on the sensitivity baseline,the resistance index of each C.gloeosporioides to azoxystrobin was calculated.The results showed that there were 163 sensitive isolates,6 low resistant isolates,4 moderate resistant isolates and 1 high resistant isolate.The number of resistant isolates was 11,accounting for 6.32% of the total population.The adaptability of resistant isolates to thiophanate-methy was not significantly different from that of sensitive stra ins due to the resistant isolates had no significant differences in biological characteristics.No single gene mutation was found at amino acid at position 120-155 of cytb.