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Transfer of Heat Tolerance and Other Characteristics by Protoplast Fusion in Trichoderma Species

L.E. Hanson and C.R. Howell


 
ABSTRACT

Several Trichoderma virens (Gliocladium virens) strains give good biocontrol activity against Rhizoctonia solani on cotton seedlings. However, these strains lack several characteristics that are required to make them commercially viable. For example, most cannot survive an entire season on the roots of a cotton plant in Texas. Also, the ability to control diseases early in the season is reduced by cool weather. Diseases such as damping-off by Pythium species and Thielaviopsis root rot are of particular interest. Other species of Trichoderma have tolerance to higher and lower temperatures than T. virens, but are not as effective as biocontrol agents on cotton. Protoplast fusion is a method that has been used in Trichoderma to successfully incorporate desirable characteristics and improve biological control efficacy. We used three effective biological control strains of T. virens in protoplast fusions with two cold tolerant strains of T. harzianum and a heat tolerant strain of T. pseudokoningii in an effort to develop improved biological control strains. Fourteen isolates that were stable through multiple transfers were obtained. One isolate was obtained that sectored into two distinct types after several transfers. Of eight fusants between T. virens and T. pseudokoningii, seven were morphologically T. virens and one was T. pseudokoningii. The T. pseudokoningii fusant had greater biological control activity against Rhizoctonia solani on cotton than the T. pseudokoningii parent and grew equally well at 40° C. All of the T. virens fusants grew significantly faster than the T. virens parent at 40° C. One of the seven T. virens fusants was significantly reduced in biological control activity compared to the T. virens parent. The T. virens and T. harzianum fusions yielded three T. virens isolates and three T. harzianum isolates. They also yielded one isolate that originally was morphologically T. harzianum, but after five transfers on selective media, sectored into T. harzianum and T. virens. The three T. virens fusants did not differ significantly from the T. harzianum parent in biological control activity against either R. solani or Pythium ultimum. However, one T. virens fusant grew significantly faster than the parent strain at 10° C. All of the T. harzianum fusants grew more slowly at 10° C than the T. harzianum parent. Some of the isolates obtained also differed from the morphologically similar parent in other characteristics, such as fungicide resistance and/or production of secondary metabolites. These results indicate that protoplast fusions can be used to alter heat tolerance in Trichoderma and that a variety of progeny can be isolated from these fusions. The above mentioned isolates are being tested for their ability to remain viable and effective in storage. Further fusions are being performed to incorporate other characteristics into isolates, and isolates are being tested for their ability to control other diseases.



Reprinted from Proceedings of the 1999 Beltwide Cotton Conferences pp. 105 - 106
©National Cotton Council, Memphis TN

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Document last modified Monday, Jun 21 1999