An-Najah Staff

The effect of indigenous Trichoderma isolates against the soil-borne phytopathogen Rhizoctonia solani was investigated in dual culture and bioassay on bean plants. Ap- plication of the bioagent isolates as a conidial suspension (3*107) greatly reduced the disease index of bean plants caused by R. solani in different rates and the most effective Trichoderma harzianum isolate (Jn14) reduced the disease by 65%. In dual culture, the T. harzianum (Jn14) overgrew the pathogen R. solani in an average of 16.75 mm/day at 30 °C. In addition, the results showed that T. harzianum (Jn14) and T. hamatum (T36) were the most effective isolates at 25°C and inhibited R. solani mycelial growth by 42% and 78% respectively, due to fungitoxic metabolites production. The Effect of Trichoderma on bean seedlings growth was obvious; height was nearly doubled (160% - 200%), while fresh and dry weights increased by 133% and 217%, respectively. Ger- mination of bean seeds in treated soil with Trichoderma isolates occurred about four days earlier than those in untreated soils. The results revealed however some variation between isolates which was due to genetic variation, mycelium-coiling rate, sporulation rate, fungitoxic metabolites, induced growth response and temperature effect.

Mycoparasitic Pythium species with spiny oogonia were surveyed in 50 Palestinian agricultural fields subject to different cropping practices using the Sclerotia Bait Technique (SBT) and the Surface-Soil-Dilution-Plate method (SSDP) with the selective VP3 medium. The mycoparasitic Pythium species were obtained from 21 (42%) soils using the SSDP method and from 37 (74%) soils using SBT. Pythium acanthicum and P. oligandrum were isolated by both methods, whereas P. periplocum was isolated only by the SBT. Using a newly modified dual plate culture method (MDPCM), the three mycoparasites showed varying antagonistic performance against several Pythium host species under a range of in vitro conditions. However, P. periplocum and P. oligandrum were found to be active biocontrol agents against P. ultimum, the damping-off organism of cucumber. This pathogen was antagonized, on thin films of water agar, by the three mycoparasites, and was moderately susceptible to P. periplocum while slightly susceptible to P. acanthicum and P. oligandrum. In direct application method in which antagonistic mycoparasites were incorporated into peat/sand mixture artificially infested with P. ultimum under growthroom conditions, Pythium oligandrum and P. periplocum (at 500 CFUg-1) significantly improved seedling emergence and protected seedlings from damping-off. In the seed coating method, biocontrol by two types of seed dressing (homogenateor oospore coated seeds), was comparable to that achieved by direct application.