玉米丝黑穗病防治研究

玉米丝黑穗病是白城地区的重要病害,一般发病率为3—5%,重者高达30%以上,是生产上急待解决的问题。其症状以正常型为主,有时出现矮化型、矮化丛生型和多分蘖型等特异症状。病株以雌穗为黑穗、雄穗为健穗及雌雄穗皆为黑穗者居多。病穗上自然脱落的厚垣孢子萌发率高,病穗内的萌发率明显降低。此病为系统侵染病害,种子及土壤均可带菌传病,以土壤带菌为主,属土传病害。厚垣孢子在土壤里能存活三年,土壤带菌量越多,菌土覆盖种子越厚,发病率越高。丝黑穗病菌侵染玉米幼苗时间较长,从种子萌芽到四叶期最易侵染,五叶期后,侵染明显下降,八叶期后不再侵染。在幼苗叶片上接菌不能侵染致病。玉米丝黑穗病菌不能侵染高梁。高梁丝黑穗病菌能侵染玉米,但侵染率甚低。侵染玉米后的病菌,不再侵染高梁,只侵染玉米,且致病力明显增强。两菌是同一菌种的不同生理型。用来自九个省、市的丝黑穗病菌接种于不同抗性的自交系鉴定寄主,其致病力不同,陕西和新疆的致病力弱,辽宁和吉林的致病力强。在田间人工接种条件下,鉴定了二百余份自交系和杂交种的抗病性,品种间有明显差异,高抗的近于免疫,高感的发病率在90%以上。抗病性遗传规律表现为双亲高抗的,其后代亦抗,以母本的抗病性起主导作用。选百余种农药处理种子,筛选结果:个别药剂防效有高达70%以上者,但年度间效果不稳定,多数药效稳定在50%左右。

ON THE CONTROL OF HEAD SMUT OF CORN

The head smutSphacelotheca reiliana(Kühn)Clint.]of corn is one of the most important diseases in BaiCheng region of Jilin province.The percentage of smut plant is usually about 3-5%,and sometimes over 30%.The symptoms besides the ordinary stunting,rosetto and polystooling were observed.The smut balls occur mostly on ears and sometimes on both ears and tassels.Chlamydospores collected from natural dissemination showed a high percentage of germination,but those collected from inner part of the sorus were low in germination.Although it might be carried on seedcoat yet soil transmission is considered to be the main mode of dissemination since the chlamydospores maintained their vitality in soils for three years.Higher infections might be obtained from the contaminated soil.Infections in seedling stage occurred abundantly until 4 leaf stage,and actually decreased since the starting of the 5 leaf stage and no infection took place at leaf stage.Head smut fungus from corn did not infect sorghum.On the contrary corn plants were to be infected by sorghum head smut with a low rate.The chlamydospores thus produced from corn plants lost the ability to infect sorghum,however infected corn in an increasing rate.It might be due to the different physiological races in the smutinoculum.The head smut fungus collected from Shanxi and Xinjiang were weak in pathogenicity and those from Liaoning and Jilin are strong.More than 200 inbred lines and hybrids had been tested for their resistance to head smut in field plots.The high resistant varieties were almost immune.The resistance of maternal plants had more important infleunce to next generations.Over hundred fungicides tested for seed treatment,a few of them showed 70% controlling effects and were not stable in different years.Most fungicides only showed 50% controlling effects.