Pervaiz A. Abbasi

Effect of compost amendments on disease severity and yield of tomato in conventional and organic production systems

Field trials were conducted over 2 years to assess the effects of compost amendments on disease development in organic and conventional processing tomato (Lycopersicon esculentum L.) production systems. The incidence of anthracnose fruit rot was reduced in organic tomato plots amended with a high rate of composted cannery wastes compared with the incidence in nonamended control plots in 1998 when disease incidence was high. Marketable yield was increased by 33% in compost-amended organic plots. Plots amended with a high compost rate had more ripe fruit than the nonamended control. The incidence of anthracnose and of total disease on fruit was less on the cultivar OH 8245 than on Peto 696. Total fruit yield of OH 8245 but not Peto 696 in organic plots was increased by amendment with composted cannery wastes. In conventional tomato production, composted yard wastes increased disease severity on foliage both years but reduced bacterial spot incidence on fruit in 1997, when disease pressure was high. The incidence of anthracnose was not affected by composted yard wastes. Marketable and total fruit yields of Peto 696 were not increased in compost-amended conventional plots. The plant activator Actigard reduced foliar disease severity and the incidence of bacterial spot and anthracnose on fruit, while increasing yield of marketable fruit.

Suppression of Bacterial Spot of Tomato with Foliar Sprays of Compost Extracts Under Greenhouse and Field Conditions

The efficacy of foliar sprays with compost water extracts (compost extracts) in reducing the severity of bacterial spot of tomato caused by Xanthomonas vesicatoria was investigated. Extracts prepared from composted cow manure, composted pine bark, an organic farm compost, or composted yard waste, applied as foliar sprays on tomato transplants, resulted in a moderate but statistically significant reduction in the severity of bacterial spot. The population of X. vesicatoria in infected leaves was reduced significantly by extracts prepared from composted cow manure. Efficacy of the water extracts was not affected by oxygen concentrations in the suspension during extraction, compost maturity, or sterilization by filtration or autoclaving. The degree of control provided by foliar sprays with the most effective compost extracts did not differ from that obtained with the plant activator acibenzolar-S-methyl. In the field in two growing seasons, foliar sprays with compost water extracts did not reduce the severity of foliar diseases, including bacterial spot. During the 1997 season, when the severity of bacterial spot in the field was high, foliar sprays with compost water extracts significantly reduced the incidence of bacterial spot on tomato fruit. Amending plot soil with several rates of composted yard waste did not lead to additional control of fruit disease over those only sprayed with extracts. Foliar sprays with a mixture of chlorothalonil and copper hydroxide or with acibenzolar-S-methyl reduced the severity of bacterial spot as well as incidence of spot on fruit.

SUPPRESSION OF RHIZOCTONIA AND PYTHIUM DAMPING-OFF OF RADISH AND CUCUMBER SEEDLINGS BY ADDITION OF FISH EMULSION TO PEAT MIX OR SOIL

The efficacy of fish emulsion in enhancing plant growth and suppressing seedling damping-off diseases caused by Rhizoctonia solani and Pythium aphanidermatum was investigated on peat mix and soil. Fish emulsion (1%–4%; m/m peat mix) or equivalent inorganic fertilizer (N–P–K) was incorporated into pathogen-infested peat mix and incubated in plastic bags for 1, 7, 14, and 28 days prior to planting radish or cucumber seeds. Plants were rated 14 days later for incidence and severity of damping-off. Negligible protection of seedlings from damping-off occurred in peat mix incubated for 1 day with fish emulsion. After 7 days incubation, however, 70%–80% of the seedlings remained disease-free in peat mix amended with 4% fish emulsion. After 28 days, equivalent levels of disease protection were found with all concentrations of fish emulsion. As the inorganic N–P–K treatment was adjusted to reflect N–P–K levels in the fish emulsion, no disease control was obtained, indicating that disease protection was not due to increased plant nutrition. Incorporation of 0.5% (m/m soil) fish emulsion into soil 5 days before planting radish provided effective control of damping-off disease. Fish emulsion (2% and 4%; m/m muck soil) also effectively and consistently suppressed damping-off of cucumber seedlings in muck soil naturally infested with damping-off pathogens. Pasteurization of the peat mix followed by re-infestation with R. solani resulted in a much higher level of disease than that obtained in unpasteurized infested peat mix. Addition of fish emulsion resulted in restoration of disease suppression within 7 days. These results suggest that fish emulsion may not be toxic to the pathogens but may create a biological climate in peat substrate or soil that is suppressive to the disease. Fresh and dry mass measurements of plants produced in 4% fish emulsion were 2 to 3 times greater than in nonfertilized peat but were comparable with those receiving equivalent N–P–K. The results suggest that fish emulsion has both nutritive value for plant growth as well as disease suppressive properties. Thus, it may be an ideal product for use in organic or conventional transplant production.

Reduction of bacterial spot disease severity on tomato and pepper plants with foliar applications of ammonium lignosulfonate and potassium phosphate

Bacterial spot is a serious and persistent disease problem of tomato and bell pepper in both the United States and Canada. Current disease management practices, based primarily on fixed copper bactericides, do not give consistent, effective protection. Foliar applications of ammonium lignosulfonate (ALS), derived from the wood pulping process, and the fertilizer potassium phosphate (KP) were tested for their ability to control this disease under both greenhouse and field conditions. Acibenzolar-S-methyl was included as a control. Greenhouse-grown tomato transplants treated with acibenzolar-S-methyl, 2 or 4% (vol/vol) ALS, 25 mM KP, or 2% ALS plus 10 mM KP and then inoculated with Xanthomonas campestris pv. vesicatoria had significantly less disease than the unprotected controls. Weekly foliar applications of acibenzolar-S-methyl, ALS, or KP significantly reduced disease severity on the foliage of inoculated field-grown tomato and pepper plants; although less disease appeared on the fruit of these plants, the effect was not always statistically significant except for the acibenzolar-S-methyl treatment. Acibenzolar-S-methyl increased the yield of marketable tomato fruit in 2 of 3 years of the study and that of pepper fruit in 1 of 2 years. There was a marked increase in the yield of marketable fruit on all ALS-treated pepper plants in 2001. None of the treatments significantly increased total tomato or pepper yield. ALS and KP had no observable phytotoxic effect on tomato or pepper foliage. Our results indicate that future integrated disease management programs for bacterial spot may be enhanced by including foliar sprays of these two products.

Diversity Among Strains of Xanthomonas campestris pv. vitians from Lettuce

ABSTRACT Diversity in host range, pathogenicity, phenotypic characteristics, repetitive extragenic palindromic polymerase chain reaction (rep-PCR) profiles, and sequence of the 16S-23S rDNA spacer region was examined among 44 Xanthomonas strains isolated from lettuce. Forty-two of the strains were divided into two groups, designated A and B. Seventy percent were Group A, and most of the remaining strains including a reference strain (LMG 938) were Group B. Group A strains induced both local and systemic symptoms, whereas Group B strains caused only distinct necrotic spots. Two strains, including the X. campestris pv. vitians type strain, were distinct from the Group A and B strains and were not pathogenic on lettuce. Analysis of fatty acid profiles, serotype, carbon substrate utilization patterns, and protein fingerprints confirmed this grouping. The Group A and B strains also formed two unique clusters (I and II) by rep-PCR profiling that corresponded to the two groups. Direct sequencing of a PCR-amplified DNA fragment (680 bp) from the 16S-23S rDNA spacer region of four representative strains, however, did not differentiate these groups. Serology and rep-PCR fingerprinting can be used to diagnose and identify X. campestris pv. vitians strains, while the other analyses evaluated are useful for strain characterization.

Effect of foliar applications of neem oil and fish emulsion on bacterial spot and yield of tomatoes and peppers

Foliar applications of neem oil and fish emulsion, derived from neem seed and menhaden fish, respectively, were tested for their ability to reduce bacterial spot of tomato and bell pepper under both greenhouse and field conditions. Greenhouse-grown tomato and pepper plants sprayed with aqueous suspensions (0.5%, v/v) of neem oil or fish emulsion and then inoculated with Xanthomonas campestris pv. vesicatoria showed less disease symptoms than the water-treated controls. Weekly foliar sprays of neem oil and fish emulsion reduced disease severity on the foliage of inoculated field-grown tomato and pepper plants in both years of a two-year study. The disease incidence on the fruit of these plants was reduced but the effect was not always statistically significant. However, the number of lesions per pepper fruit were consistently lower with these treatments. Fish emulsion increased healthy and total fruit yield of tomatoes in 2000 and healthy fruit yield of peppers in 2001, whereas neem oil increased the yield of disease-free peppers in both years. Neem oil and fish emulsion had no observable phytotoxic effect on tomato or pepper foliage in the field. These results suggest that disease-management programs for bacterial spot may be enhanced by including foliar sprays of these products.

Effect of neem cake soil amendment on reduction of damping-off severity and population densities of plant-parasitic nematodes and soilborne plant pathogens

The effects of neem cake, a nutrient-rich organic material derived from neem seed, on plant-parasitic nematodes, Verticillium dahliae, and seedling damping-off diseases caused by Rhizoctonia solani and Pythium aphanidermatum were investigated. In greenhouse trials, 1% neem cake (mass/mass soil) caused a 67%–90% reduction in the number of lesion (Pratylenchus penetrans) and root-knot (Meloidogyne hapla) nematodes in tomato roots grown in three different soils. In the field, 1% neem cake (mass/mass soil) reduced the number of lesion nematodes by 23% in corn roots and 70% in soil around roots. Population densities of free-living nematodes were either enhanced or not affected by neem cake treatment. In laboratory tests, addition of 3% neem cake (mass/mass soil) to soil killed V. dahliae microsclerotia and increased soil pH from 5.2 to 8.7. Killing of microsclerotia appeared to be caused by generation of ammonia during decomposition of neem cake. In growth room assays, addition of 2% neem cake (mass/mass peat-based mix) to R. solani -infested peat-based mix 28 days before planting radishes reduced damping-off severity. In a sandy loam soil artificially infested with R. solani and a muck soil naturally infested with damping-off pathogens, addition of 0.5% neem cake (mass/mass soil) had no immediate effect on damping-off, whereas incubation of the amended soil for 7 days before planting radish or cucumber reduced damping-off severity. This suggested that neem cake was not directly toxic to the damping-off pathogens but that during incubation neem cake may have created a biological climate that was suppressive to disease.

Reduction of bacterial leaf spot severity on radish, lettuce, and tomato plants grown in compost-amended potting mixes

Compost-amended substrates offer the potential for management of diseases caused by soilborne as well as foliar plant pathogens. In this study, the efficacy of composted pine bark mix fortified with the biocontrol agent Trichoderma hamatum 382 (FCPB) against bacterial leaf spot of radish, lettuce, and tomato under controlled environment conditions was evaluated. Plants grown in the FCPB mix and inoculated with bacterial leaf spot pathogens were less severely diseased than plants grown in commercial peat mix or vermiculite. In some cases, plants were also grown in a composted cow manure mix or in a steam-treated compost-amended greenhouse soil, and these plants were also less severely diseased. Infected radish and tomato plants grown in these compost-amended substrates also harbored significantly smaller populations of Xanthomonas campestris pv. armoraciae and Xanthomonas campestris pv. vesicatoria, respectively. The disease-suppression effect of the FCPB mix was lost by autoclaving and restored by reinoculating the autoclaved FCPB mix with nonautoclaved FCPB mix. However, the disease-suppression effect varied among the batches of FCPB mix used. In contrast, vermiculite and a highly decomposed sphagnum peat mix consistently failed to suppress these diseases. These results suggest that producing vegetable seedlings in FCPB mix or compost-based substrates may provide initial protection against bacterial leaf spot pathogens.

Reduction of potato scab and verticillium wilt with ammonium lignosulfonate soil amendment in four Ontario potato fields

Single applications of ammonium lignosulfonate (ALS, ca. 6 t solids/ha) were made at four commercial potato fields in Ontario (sites K, V, W, and G in 1998, 1999, 2000, and 2000, respectively). Potato tubers were planted 2-4 weeks after ALS incorporation. The effects on potato scab, verticillium wilt, tuber yield, soil chemistry, and soil microbiology were determined in the year of application, and for a second crop at sites K (1999), V (2000), and G (2001). Potato scab severity was significantly reduced (50-80%) by ALS treatment in the year of application at all sites. Significantly less scab was present for the second crop at sites K and G. The incidence of Verticillium dahliae infected plants was also significantly decreased (40-50%) by ALS treatment at all sites in the year of application and for the second crop at site K. Ammonium lignosulfonate significantly increased total tuber yield by 2.5 times at site G in 2000. There was no effect on tuber yield at the other sites. However, marketable yield (tubers with <5% surface scab) was significantly increased three- to seven-fold over the control plots at all sites in the year of application. Although marketable yield was consistently higher in subsequent crops at all sites, it was only statistically significant at site G. Soil pH was immediately reduced following application of ALS by 0.4-0.6 units at all sites except site W, where it had no effect. Soil pH returned to control levels by the second season at all sites except site G, which remained one log unit lower than the control treatment. Numbers of soil microorganisms increased two- to eight-fold at all sites within weeks of ALS application. Fungal numbers increased the most and remained elevated for two seasons at site K compared with control plots. The results of this study clearly demonstrate that use of ALS as a soil amendment can significantly reduce the severity of potato scab and verticillium wilt in potato crops.

Effect of fish emulsion used as a preplanting soil amendment on verticillium wilt, scab, and tuber yield of potato

Fish emulsion is used mainly as a fertilizer for crop production but, in a previous study, we have demonstrated its efficacy in suppressing damping-off [Rhizoctonia and Pythium spp.] in radish and cucumber in a peat-based substrate or soil. In the present study, fish emulsion was tested as a preplanting soil amendment to control soilborne diseases of eggplant and potato such as verticillium wilt [Verticillium dahliae and Verticillium albo-atrum] and scab [Streptomyces spp.]. Tests were conducted on 11 soils with different characteristics (pH, 5.2–7.2; organic-matter content, 1.0%–3.7%), originating from commercial potato fields in Ontario, New Brunswick, and Prince Edward Island with a history of verticillium wilt and scab. The amendment of soil with fish emulsion at rates of 0.5% and 1% (m/m) protected eggplant from verticillium wilt, and the 1% fish-emulsion treatment increased fresh and dry plant biomasses in the greenhouse. Microplot experiments with potato showed that the 1% fish-emulsion treatment significantly (P < 0.05) reduced scab severity (by 0.6–2.1 units on a scale of 0–6) in seven soils with low to moderate scab-disease pressure and significantly increased total tuber yield (by 41%–170%) in nine soils, compared with the control treatments. Fish emulsion also reduced potato petiole infection by V. dahliae in one soil. In potato field trials at two sites in 2004, treatment with 1% fish emulsion (20 000 L/ha) significantly (P < 0.05) reduced scab severity (by 0.8–1 units) and significantly increased scab-free tubers (by 132%–366%) and marketable-tuber (surface scab < 5%) yield (by two fold), compared with the control treatments. Total tuber yield was reduced at one site and not affected at the other. No effect of fish emulsion on scab and verticillium wilt or tuber yield was observed in a 2005 field trial. The reduction of scab or verticillium wilt by fish emulsion was not soil-specific and varied from year to year. The results indicated that fish emulsion was not effective in soils with high disease pressure.