Non-solarized Soil Research Articles

Reductions in Inoculum Density ofRhizoctonia solaniand Control of Belly Rot on Pickling Cucumber with Solarization

The effectiveness of soil solarization to reduce the level of Rhizoctonia solani in soil and control belly rot on cucumber fruit was evaluated in naturally infested soil. Solarization under clear polyethylene mulch for 5 to 6 weeks during July and August 1992 to 1994 was compared with application of chlorothalonil and no treatment in a randomized complete block design. During solarization in 1993 and 1994, the percentage of organic matter colonized by R. solani declined at 0 to 10 cm depth in solarized soil but did not change significantly in nonsolarized soil. After solarization, colonies of R. solani grew from 0.9, 7, and 2.8% of the organic matter fragments recovered from solarized soil in 1992, 1993, and 1994, respectively, compared with 23, 44, and 26% of the organic matter from nonsolarized soil. Population densities of fluorescent Pseudomonas spp. at 0 to 20 cm declined during solarization each year. In 1992 and 1994, thermotolerant fungi, which grew at 40°C, were more abundant in solarized than nonsolarized soil. Penicillium spp. accounted for a significantly greater percentage of thermotolerant fungi in heated than in nonheated soil each year. Solarization reduced belly rot severity on pickling cucumber in 1992 and 1994 compared with no treatment (4.8% versus 10.1% and 4.4% versus 12.9%, respectively), whereas chlorothalonil reduced severity in 1993 (4.0%) and 1994 (4.1%). Incidence of belly rot was reduced by solarization and chlorothalonil applications in 1993 and 1994 but not in 1992. Neither treatment significantly increased total weight of healthy fruit compared with the control. In 1994, healthy fruit in solarized plots had a higher market value than fruit in plots of the other two treatments, but after cost of the treatments was subtracted, returns did not differ. Soil solarization is an effective nonchemical method for reducing preplant levels of R. solani.

Suppression of Major and Minor Pathogens by Fluorescent Pseudomonads in Solarized and Nonsolarized Soils

Strains of fluorescent pseudomonads increased the growth of tomato plants in nonsolarized soil but not in solarized soil. Vital staining showed that fluorescent pseudomonads colonize the root cortex and, apparently, internally colonize the younger lateral roots of artificially inoculated plants growing in nonsolarized soil. The minor pathogen Penicillium pinophilum caused growth retardation of tomato and cotton plants. It colonized tomato roots in nonsolarized, methyl bromide-fumigated, and solarized soils (to a much lesser extent). Inoculation of tomato roots with fluorescent pseudomonads or transplanting tomato roots to solarized soil suppressed colonization by Penicillium pinophilum and nullified plant-growth retardation []

Influence of Seed and Root Exudates on Fluorescent Pseudomonads and Fungi in Solarized Soil

We investigated the effect of soil solarization on seed and root exudates of tomato plants and the role of these exudates in the establishment of fluorescent pseudomonads in soil. Seed and root exudates of tomato grown in solarized soil contained lower amounts of sugars and higher amounts of amino acids and amino compounds and were less favorable for growth of bacteria and fungi in culture compared with seed and root exudates of tomato grown in nonsolarized soil. Addition of exudates from germinating seeds into solarized soil, however, increased populations of fluorescent pseudomonads and decreased populations of fungi compared with nonsolarized soil (...)

Chemotaxis of Fluorescent Pseudomonads Towards Seed Exudates and Germinating Seeds in Solarized Soil

We investigated the chemotaxis of fluorescent pseudomonads towards seeds exudates and germinating tomato seeds. Chemotaxis of Pseudomonas putida and P.fluorescens in a capillary tube was more pronounced towards exudates originating from seeds that were germinated in solarized soil than towards comparable exudates from seeds that were germinated in nonsolarized soil. Movement of these bacteria was enhanced also towards a mixture of either amino acids or amino acids and sugars, but not of sugars alone (...)

Soil Polarization and Dacthal: Influence on Weeds, Growth, and Root Microflora of Collards

Soil polarization for 98 days in 1985 resulted in a 91% reduction of weeds present in collard greens (Brassica oleracea acephafa L.) plots during 1986. Soil solarization was more effective in controlling weeds in collard green plots when compared to an application of Dacthal-75W herbicide in nonsolarized plots. Collard green plants grown in solarized soil showed an increase in yield and other growth responses. Soil samples from the rhizosphere of plants grown in solarized soil showed higher population levels of bacteria and thermotolerant fungi than from nonsolarized soil. There were significant negative responses in marketable yield and root growth of collard greens and in soil microflora in solarized soil in response to Dacthal-75W herbicide application. Chemical name used: dimethyltetrachloroterephthalate (Dacthal-75W).

Fertility and management practices to control verticillium wilt of the russet burbank potato

Management practices for the suppression of Verticillium wilt of Russet Burbank potato include sanitation, use of optimum sprinkler-irrigation practices, soil solarization, and an adequate soil fertility program. Among all cultural factors considered, nitrogen (N) deficiency in potato tissue was most commonly associated with the severity of Verticiilium wilt in Russet Burbank potato. Field studies have shown that increased N availability suppresses Verticiilium incidence on cv Russet Burbank while having no effect on cv Norgold Russet. Studies from both greenhouse and field show that the colonization ofV dahliae in potato stem tissue is suppressed in cv Russet Burbank when the availability of Phosphorous (P) is increased to the optimum. Following one season of cropping with Russet Burbank potato, the treatment providing the optimal N availability also suppressed the increases ofV dahliae populations in the soil during the following year of consecutive cropping. Similarly, after two seasons of continuous potato cropping, treatments with optimal P had lower soil populations ofV. dahliae in soil. Results show the suppression of Verticiilium wilt with optimal fertility. Verticiilium wilt [caused by eitherVerticiilium dahliae Kleb, (microsclerotial form) orVerticiilium albo- atrum Reinke and Berthold (dark mycelial form)] is one of the most severe diseases of potato in the United States. Potato yields, tuber size, and specific gravity may be substantially reduced by this disease, depending on severity, time of occurrence, and growing season. In Idaho and other arid growing regions of the United States, Verticiilium wilt is caused byVerticillium dahliae Kleb. Idaho field studies involving cropping practices, soil fumigation treatments, solarization, and Verticillium-resistant potato clones all support the importance ofV dahliae upon potato yield. Data from these studies show that yield losses due toV. dahliae commonly approximate 5 to 12 metric T/ha (5, 6). Table 1 illustrates the effect of several cropping practices upon relativeV dahliae populations in soil with the effects upon both disease severity and potato yield. With continuous cropping of Russet Burbank,V dahliae populations in soil increased, and yields were reduced by 18 to 19 metric Tlha when compared to locations that had been allowed to remain either weed-free and fallow or where corn had been previously cropped. It was estimated thatV dahliae was influencing yield by about 10 to 12 metric Tlha based on a regression analysis of yield as a function ofV dahliae populations in soil. Similarly, whenV dahliae was suppressed by fumigation treatments involving mixtures of dichloropropene and picfume, yields more significantly increased by 6.5 to 12 metric T/ha (5). Although many factors may influence yields, clones with higher Verticillium resistance than Russet Burbank generally out-yield Russet Burbank. Figure 1 demonstrates the effect of solarization (a technique involving the laying of clear plastic on soil for the purpose of elevating soil temperatures to killV dahliae). When Verticillium was controlled in this manner (lo), there was no significant yield difference between the Russet Burbank potato and the highly resistant A68113-4 clone. The A68113-4 clone grown in non-solarized soil out-yielded the Russet Burbank in non-solarized soil by 31 percent while the solarization treatment significantly increased yield for the Russet Burbank and A68113-4 clones by 46 and 18 percent, respectively. These yield responses were observed in a field where inoculum levels ofV dahliae were relatively low (2.10 cfulgrn of soil). With these losses, the need to develop control procedures is great and to achieve this control the need also exists to accurately evaluate the effect of treatments uponV dahliae. Our Idaho studies have routinely utilized such a procedure (9) in combination with comparisons of both disease severity and yield.