Wen-Chuan Chung

Effect of ground Brassica seed meal on control of Rhizoctonia damping-off of cabbage

Ten cultivars of three Brassica species were compared for volatile compounds in hydrated ground seeds that were fungicidal to Rhizoctonia solani AG-4. Among the samples tested, the volatile substances in the ground seed of mustard (Brassica juncea cv. Bau Sin) showed the strongest fungicidal effect. Allyl isothiocyanate was one of the predominant fungicidal compounds detected in the ground seed of all Brassica species tested, and the amount was the highest in ground mustard seed meals. Among the nine carriers tested for seed coating with ground mustard seed meal, Biolan peat B3 was the most effective for the seed treatment. Cabbage seeds treated with a mixture of ground mustard seed meal and Biolan peat B3 (MBF mixture) at 2:3 ratio (w/w) resulted in a significant reduction in incidence of Rhizoctonia damping-off with no harmful effects to the germination of treated seeds. Effective control of Rhizoctonia damping-off of cabbage by the seed treatment with the MBF mixture was also obtained in a large-scale experiment conducted in a commercial automated environment-controlled greenhouse. This study suggests that the MBF mixture has potential for use in the commercial seed treatment.

Organic amendment of commercial culture media for improving control of Rhizoctonia damping-off of cabbage

Rhizoctonia solani AG-4 is an important damping-off pathogen of cabbage. Using a baiting technique, R. solani was recovered from the cabbage seeds buried in nine commercial culture media. The frequency of seed colonization by R. solani varied with medium, ranging from 2.5% in Nev-3 to 30% in Floradur A and SI 2; the seeds were examined after being buried for 48 h. Among the five formulated organic compounds tested as amendment for the commercial BVB No. 4 medium, FBN-5A was most effective in controlling damping-off. Although both rates of FBN- 5A, 0.1% and 0.2%, significantly reduced incidence of damping-off, FBN-5A at 0.1% was the more suitable treatment because it not only reduced the disease incidence, but also enhanced the growth of cabbage. The results were confirmed in a large-scale experiment in a commercial automatic environment-controlled greenhouse. This study suggests that the FBN-5A compound offers potential for commercial use as an organic amendment for the management of Rhizoctonia damping-o...

Control, by Brassica seed pomace combined with Pseudomonas boreopolis, of damping-off of watermelon caused by Pythium sp.

A total of 57 isolates of fungi, bacteria, and actinomycetes were screened for their ability to degrade the glucosinolate sinigrin. Pseudomonas boreopolis was the most effective among 26 isolates having the capacity to degrade sinigrin. Treatment with ground Brassica seed pomace and Pseudomonas boreopolis resulted in the release of volatile compounds. Gas-chromatography analyses allowed to identify allyl isothiocyanate and 3-butenyl isothiocyanate as the major volatile compounds released from enzymatic hydrolysis of glucosinolates by Pseudomonas boreopolis. These compounds had strong fungicidal activity against Rhizoctonia solani AG-4, Sclerotium rolfsii, Sclerotinia sclerotiorum, Pythium aphanidermatum, and Phytophthora capsici as revealed by reduced mycelial growth. They were also responsible for reducing the survival of zoospores and oospores of P. aphanidermatum. A large-scale greenhouse trial showed that amendment of growth media (Bas Van Buuren medium No. 4, 7mL; soil, 3 g) with 1% (mass fraction) of the ground Brassica seed pomace and Pseudomonas boreopolis (1 × 108 to 1.8 × 108 cfu/mL) was effective in controlling damping-off of watermelon caused by Pythium sp., resulting in increased production of healthy, marketable seedlings.

Inhibition of Penicillium digitatum and Citrus Green Mold by VolatileCompounds Produced by Enterobacter cloacae

Penicillium digitatum causes green mold decay on citrus fruit, resulting in severe economic losses to citrus growers and packers worldwide. The present study is to evaluate the control of citrus green mold by volatiles produced by Enterobacter cloacae. An E. cloacae strain isolated from plant rhizospheres was able to produce three volatile organic compounds, which were identified as butyl acetate, phenylethyl alcohol, and 4,5-dimethyl-1-hexene by GC/MS chromatography. The volatile compounds produced by E. cloacae inhibited conidial germination and hyphal elongation of P. digitatum and reduced green mold severity. E. cloacae cultured at temperatures ranging from 16°C to 28°C, at pH values ≤6, or in a substrate carrier (sphagnum moss, vermiculite, or perlite) provided superior control against P. digitatum. A laboratory formulation using E. cloacae and perlite protected citrus fruit from green mold up to 22 days and its effectiveness outperformed fungicide application at room temperature (~25°C). The results implicate practical application of E. cloacae as a biofumigant for controlling citrus postharvest decay caused by P. digitatum. Significantly, the study provides a model for future research on how to formulate an effective biocontrol agent for disease management.

Effects of nutrients on production of fungichromin by Streptomyces padanus PMS-702 and efficacy of control of Phytophthora infestans

The effects of carbon and nitrogen source on inhibitory activity of Streptomyces padanus PMS-702 culture filtrates were investigated using 12 saccharides, 12 nitrogen sources, and 7 organic compounds. Results showed that the carbon sources cellobiose, galactose, glucose, mannose and xylose; the organic compound peanut meal; and the nitrogen source glutamic acid were the most effective components for production of inhibitory substances by S. padanus and suppression of zoospore release of Phytophthora infestans. Production of the antibiotic fungichromin by S. padanus PMS-702 was high (145.5 ppm) in cultures grown in the liquid medium of peanut meal – glucose – glutamic acid (PMGG) containing 1.5% (w/v) peanut meal, 0.5% (w/v) glucose, and 0.5% (w/v) glutamic acid for 7 days. Spraying tomato plants with culture filtrates of S. padanus PMS-702 from the PMGG broth culture at a rate of 100-fold dilution significantly reduced severity of late blight of tomato (Lycopersicon esculentum) foliage caused by P. infestans both under controlled environment and field conditions.

Development of a semiselective medium for detection of Mycosphaerella pinodes in soil, plant debris and seed.

Abstract Garden pea leaf blight, caused by Mycosphaerella pinodes, is a severe disease of peas worldwide. Detection of this pathogen from seed, plant debris and soil is difficult using non-selective agar media. This study was conducted to develop a semiselective medium for the isolation of this pathogen. Of the 14 carbon sources and 18 nitrogen sources tested, maltose and soluble starch were the most suitable carbon sources and casein was the most important nitrogen source for mycelial growth of three isolates of M. pinodes. Among 13 pesticides and two antibiotics tested, atrazine, mepronil, paraquat, propamocarb and TMTD showed no adverse effect on growth of M. pinodes. Based on these results, a starch–casein semiselective medium (designated as the SC-semiselective medium) was developed by amendment of 1 L Czapek–Dox agar with 30 g soluble starch, 2 g casein, 25 μg mL-1 propamocarb, 10 μg mL-1 benomyl, 50 μg mL-1 mepronil, 300 μg mL-1 atrazine, 100 μg mL-1 streptomycin sulfate and 200 μg mL-1 neomycin sulfate. This SC-semiselective medium was effective for detection of M. pinodes in artificially and naturally infested field soils, diseased seeds, leaves, and stems of peas. It should have potential for applications in research on biology, ecology and control of M. pinodes in peas.