Studies On Identification Techniques Of Cotton For Verticillium Wilt Resistance

Verticillium wilt of cotton is one kind of fungus disease, known as "cancer of cotton". It is caused by Verticillium dahliae which infects cotton vasculars and leads to the wilt of the cotton plants, resaulting in the yield and quality decline seriously. Scholars in home and abroad generally believe that selection and utilization of resistant varieties of cotton is an economic and effective way of controlling cotton verticillium wilt. Identification of cotton resistance to Verticillium wilt is an essential part for breeding and selecting resistant materials.Identification of cotton adult plants is mainly carried out by artificial disease nursery. There are many methods for identification of cotton Verticillium wilt resistance at seedling stage, such as non-bottom plastic bottle identification, however they have some shortcomings, for example, it's hard to get the uniform degree of wounding roots.So methods on identification of cotton resistance to verticillium wilt still needs improvement and unity urgently.In order to explore a new fast, accurate and simple technique for identification of cotton resistance to verticillium wilt, techniques of cotton resistance to verticillium wilt, based on floating nursing seedling in nutrient water-bed were studied in the present paper as follows:1.Nursery plates soaked in spore suspension. It is proved that being able to distinguish between resistant and susceptible varieties more accurately, injuring 0.5cm or half hydrophilic roots are the more appropriate methods of wounding roots by hurting roots in different ways;concentration gradient experiment indicated that the more appropriate concentration of spore suspension was 1.05×107m-1;nursery plates soaked in spore suspension in different times indicated that the more appropriate time was one day. But it aways leads many cotton seedlings to death, not because of verticillium wilt, but the other reasons.As a resault, the identification effectiveness of cotton resistanc to verticilium wilt was seriously affected.2.Methods of inoculation improvement by hurting drought roots. It is proved that inserting in media along the wall of hole in plate twice with a nail is a relatively appropriate way to injury drought roots by hurting roots in different ways, because it can distinguish between resistant and susceptible varieties more accurately. But inoculation in media in nursery plates leads many cotton seedlings to death,not because of verticillium wilt, but the other reasons, which is the same as nursery plates soaked in spore suspension.3.Transplanting seedlings from nursery plates and dipping hydrophilic roots in spore suspension. Through hurting roots in different degrees, different concentration gradient and different soaking time, it had been found that the resistant and susceptible varieties could be distinguished more accurately by injuring 0.5cm or half hydrophilic roots, the appropriate concentration of spore suspension was 5×106ml-; and the proper time was one day.13 to 16 days after inoculation were the best period to survey disease process and identification of cotton resistance to verticillium wilt can last 40 to 45 days.Mortality rate of cotton seedlings after being transplanted from nursery plates was very low because the seedlings'well-developed drought roots carry media and the seedlings'recover period is very short, no more than one day generally. Transplanting seedlings from nursery plates and dipping hydrophilic roots in spore suspension is the more appropriate technique for identification of cotton resistance to verticillium wilt than any other identification techniques.4.Identification of cotton resistance to verticillium wilt with true leaves in vitro.The fungus isolated from diseased true leaves were identified morphologically, which conformed that the fungus were just the inoculated Verticillium dahliae—6sy2-37.It proved that the symptoms shown by the diseased leaves were just verticillium wilt.Concentration of spore suspension for inoculation and times dipping in spore suspension were explored in this paper. The results showed that there was no significant difference among times dipping in spore suspension at the same concentration of spore suspension, and there was also no significant difference among concentration of spore suspension at the same times dipping in spore suspension. However,disease idex between E-mian 24 and Yinrui 361 had significant difference.In accordance with the simple and convenient principle, the best appropriate times dipping in spore suspension were 1-2s and the best appropriate concentration of spore suspension was 5×106 ml-1.15 to 20 days after inoculation were the best period to survey disease process.In addition, the higher the concentration of spore suspension, the slower the roots germination, which indicated that roots germination from petiole associated with concentration of spore suspension. It is possible that toxic proteins had some inhibiting effects on roots germination.