The Occurrence Factors Of Stiffness And Cracking Bolls In Xinjiang Cotton Field

Since 2015,a large number of stiffness and cracking bolls have appeared in cotton fields in Xinjiang.The occurrence of stiffness and cracking bolls sseriously affects the quality and yield of cotton and brings huge economic losses cotton farmers.This study was carried out to clarify the factors of stiffness and cracking bolls.From 2017,the phenomenon of stiffness and cracking bolls in 20 cotton planting units in Xinjiang has been investigated.The results showed that the occurrence of stiffness and cracking bolls was common in Xinjiang cotton field,and the most serious cotton field was37%.There are obvious differences between the stiffness and cracking bolls in cotton field and the rotten bolls,such as the time of stiffeness and cracking boll is earlier than that of general rotten boll disease,the surface on boll is often formed rust-brown spot.The damage degree of stiffness and cracking boll is far greater than that of general rotten boll.F.intonsa or A.gossypii was often accompanied with stiffness and cracking boll.And some bolls surface were often covered with black or black green mould layer.Therefore,it was preliminarily determined that the the occurrence of stiffness and cracking bolls in cotton field may be related to the harm of F.intonsa,A.gossypii and other pathogen.In order to find out the relationship between the occurrence of stiffness and cracking boll and the harm of F.intonsa and A.gossypii,the cotton flowers and buds were inoculated with net bag inoculation method.It was found that the damage of F.intonsa could cause rust-brown markings on the surface of cotton boll,and the symptoms of F.intonsa inoculated on buds were more serious than that of flowers;A.gossypii was' t cause the symptom of stiffness and cracking boll,but the wounds and secreted of A.gossypii induced some fungi pathogens on the surface of cotton bolls.The black green or black stiffness and cracking bolls were separated and purified by dilution and tissue separation,and obtained two main separations: Cladosporium.and Alternaria.According to the characteristic of morphology,molecular biology and pathogenicity of strains,three species of Cladosporium were identified: C.cladosporioides,C.limoniforme and C.velox,C.cladosporioides was the dominant species;there are two species of Alternaria: A.alternata and A.tenuissima,A.tenuissima was the dominant species.The biological characteristics of different temperature,humidity,light,pH and culture medium were tested.The results showed that three species of Cladosporium had widely adaptability to environmental conditions,and their optimum growth and sporulation temperature were 20?-25?,and the optimum relative humidity of C.cladosporioides for growth and sporulation was above 80%,and the complete darkness and light-dark alternates were optimal for its growth,but light had little effect on sporulation and the optimum pH was6,and the media was PDA,OA and CBA;The optimum growth and sporulation of C.limoniforme were over 60% relative humidity,pH 8,PDA,and light had little effect on this species;the optimum relative humidity of C.velox for growth and sporulation was 60%-80%,and the light was completely darkness and light dark alternation,pH was 10,and the medium was PDA.The optimum temperature for growth and sporulation of two Alternaria was 25?-30?,the optimum relative humidity for growth was 80%,the optimum relative humidity for sporulation was 100%,and the optimum light for growth and sporulation was completely dark,the optimum growth and sporulation pH of A.tenuissima was 7,the optimum growth medium was PDA,PSA and OA,and the optimum sporulation medium was PDA;The optimum growth and sporulation pH of A.alternata was 7,the optimum medium for growth was CZ,and the optimum medium for sporulation was PDA.