C. Stevens

Plant hormesis induced by ultraviolet light-C for controlling postharvest diseases of tree fruits

Abstract Low hormetic doses of ultraviolet light (254 nm, UV-C) reduced postharvest decay of pome, stone, and citrus fruits. Loring and Elberta peaches, Golden Delicious apples, Marsh Seedless grapefruits, and Dancy tangerines were irradiated with selected low UV-C doses and stored. The application of UV-C reduced postharvest decay which included: brown rot ( Monilinia fructicola ) of peaches; Alternaria rot ( Alternaria spp.), bitter rot ( Colletotrichum gloeosporioides ) of apples and brown rot ( Monilinia spp.) of apples; green mold rot ( Penicillium digitatum ) of grape fruits and tangerines; and stem end rot ( Alternaria citri ) and sour rot ( Geotrichum candidum ) of tangerines.

The germicidal and hormetic effects of UV-C light on reducing brown rot disease and yeast microflora of peaches

Abstract The application of ultraviolet light-C doses (254 nm, UV-C) was used to determine the germicidal and hormetic effects on reducing brown rot of ‘Elberta’ peaches which were naturally and artificially inoculated with Monilinia fructicola . The results showed that a negative relationship existed between UV-C doses, colony forming units of the fungus, and the number of brown rot lesions. Also, the results of our study showed that the hormetic (beneficial) effect of low UV-C dose of 7.5 kJ m −2 induced host resistance by controlling latent brown rot infection. The hormetic effects of UV-C on peaches was photoreversed with visible light and resulted in the reduction of host resistance to brown rot. Furthermore, the results indicated that UV-C doses increased phenylalanine ammonia-lyase activity, delayed ripening and suppressed ethylene production. Additionally, the population of epiphytic yeast ( Debaryomyces hansenii ) increased curvilinearly on peach surfaces following UV-C irradiation up to 7.5 kJ m −2 . Evaluation of the yeast population on the peach surfaces showed an antagonistic activity against M. fructicola . The possibility of the host peripheral defense by UV-C stimulation of the antagonist activity of a yeast is discussed.

Integration of soil solarization with chemical, biological and cultural control for the management of soilborne diseases of vegetables

The long-term effectiveness of soil solarization integrated with (integration of pest management [IPM]) a biological control agent (Trichoderma virens), chemical fungicide (pentachloronitrobenzene [PCNB]), organic amendment (chicken litter) or physical method (black agriplastic mulch) to reduce southern blight (Sclerotium rolfsii) and southern root-knot diseases (Meloidogyne incognita) were evaluated on vegetable production. Results showed that the long-term effectiveness of IPM plus soil solarization reduced soilborne diseases of vegetables more than two years following the termination of solarization. These disease management strategies in 1991 and 1992, following soil solarization in 1990, reduced the numbers of sclerotia in the soil, and the number of plants killed by southern blight and root-knot of tomatoes, compared to nonsolarized bare soil treatment. The integration of a reduced dosage level of PCNB or T. virens in field plots, reduced southern blight of tomatoes by 100% and 71%, respectively, in solarized soil, compared to nonsolarized bare soil two years following soil solarization. PCNB effectively controlled southern blight in nonsolarized bare soil both years. All solarized treatments, except PCNB plus solarized soil increased tomato yields compared to nonsolarized bare soil plots. In the second study (1992) following soil solarization in 1991, the effectiveness of solarized bare soil, and nonsolarized bare soil mulched with black agriplastic film, with or without Reemay spunbounded polyester row cover, were effective in reducing root-knot of tomatoes as indicated by the root-knot gall index. Following a one year fallow period in 1994 three years following soil solarization, the root-knot gall index for severity of tomato roots grown in solarized bare soil, nonsolarized bare soil, black agriplastic mulched bare nonsolarized soil and black agriplastic mulched solarized bare soil, were 1.0, 3.0, 3.0 and 2.0, respectively, on a 0–5 scale, where 0=0% and 5=100% root-knot galled. In the third study 1992 and 1993, different dosage levels of chicken litter were used to amend soil artificially infested with sclerotia of S. rolfsii at different depths following solarization, decreased the number of viable sclerotia by 85–100%. All solarized treatments and nonsolarized bare soil amended with 18.8 MT/ha of chicken litter, were effective in controlling southern root-knot damage, and postharvest storage root rots of sweetpotato storage roots (Fusarium root rot [Fusarium solani] and Java black rot [Diplodia tubericola]). Our study showed that all soil solarization treatments, and soils amended with chicken litter, stimulated a shift in the soil microbial population dynamics. Rhizobacteria of Bacillus spp. and fluorescent pseudomonads increased significantly in the rhizosphere, rhizoplane, and interior root tissues of tomatoes and sweetpoatoes, grown in solarized soil compared to nonsolarized soil. These microorganisms may have contributed to the increased growth response of vegetables and some were probably suppressive to soilborne diseases

Evidence of rhizobacteria changes associated with the increased growth response of vegetables grown in agrimulch systems.

ABSTRACT Results from three vegetable experiments using agriplastic mulch systems showed a positive relationship between the increase of rhizobacteria dynamics and the increased growth response (IGR) of vegetables grown on black plastic (BM) and clear plastic (CM) mulches with or without row covers during early spring and summer. In the first experiment, no significant differences were observed for IGR of ‘Flora-dade’ tomatoes grown on bare soil following soil solarization (SBS) and nonsolarized bare soil (BS) plus BM. However, tomatoes grown on SBS, BM and BM mulched SBS plus Reemay spunbonded polyester row cover treatment showed a greater IGR compared to the non-row cover treatments. In the second experiment, plots containing ‘Crimson Sweet’ watermelons grown on CM had higher soil temperature and IGR than those grown with BM with and without VisPore row cover. When TU-82-155 swectpotato cultivar was double cropped on CM and BM plots following the removal of mulching films, sweetpotatoes showed improved yield compared to those grown in BS. In the third experiment, watermelon transplants grown on CM and BM mulches with or without VisPore row cover that were applied 21 days prior to planting had higher IGR and bacteria population in root rhizosphere than transplants grown on agrimulch systems applied just one day prior to transplanting. In all studies, there were significant increases of rhizo-bacteria in the rhizoplane, rhizosphere and root interior tissue of tomatoes and watermelons grown in solarized soil and all agrimulch systems compared to BS.