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La Mojonera, Spain

Lomas-Cano T.,University of Almeria | Boix-Ruiz A.,University of Almeria | de Cara-Garcia M.,Crop Protection | Marin-Guirao J.I.,University of Almeria | And 3 more authors.
Phytoparasitica | Year: 2016

Inoculum sources of Fusarium oxysporum f. sp. radicis-capsici and host susceptibility were studied in commercial pepper cultivars and related Capsicum spp. The pathogen could not be identified in irrigation water or in the microbiologically enriched potting medium, or associated with the seeds used in the nursery where the disease was initially reported in Spain. Although the disease was asymptomatic on older pepper plants, pathogenic strains could still be isolated from the soil of those greenhouses where the disease had been previously observed. Host susceptibility in commercial pepper cultivars and related Capsicum spp. was studied. All pepper cultivars tested (n = 19), including three rootstocks, developed symptoms when inoculated with Fusarium oxysporum f. sp. radicis-capsici. Three C. baccatum accessions and one C. annuum accession exhibited resistance, whereas two C. chinense accessions showed only partial resistance. The disease symptoms could not be distinguished from those caused by one F. oxysporum f. sp. capsici isolate, and molecular analysis also showed identical tef sequences for both formae speciales. © 2016 Springer Science+Business Media Dordrecht Source


Sibiya J.,University of KwaZulu - Natal | Tongoona P.,University of KwaZulu - Natal | Derera J.,University of KwaZulu - Natal | van Rij N.,Crop Protection
Euphytica | Year: 2012

Maize grey leaf spot (GLS) disease remains an important foliar disease in sub-Saharan Africa accounting for more than 25% yield losses in maize. Information on inheritance of GLS resistance of germplasm adapted to African environments is required in new sources being identified. Therefore, hybrids generated from a 10 × 10 half-diallel mating of tropical advanced maize inbred lines were evaluated in six environments to determine combining ability, genotype × environment interaction (G × E) and the impact of GLS disease on grain yield. General combining ability effects were highly significant and accounted for 72 and 68% of the variation for GLS resistance and grain yield, respectively. Significant specific combining ability effects associated with reduced disease levels were observed in some hybrids when one parent was resistant, and these may be exploited in developing single cross maize hybrids. Regression analysis showed a 260-320 kg ha -1 decrease in maize grain yield per each increase in GLS disease severity score, and significant associations (r = -0. 31 to -0. 60) were observed between grain yield and GLS severity scores. This showed the potential of GLS disease to reduce yield in susceptible varieties grown under favourable disease conditions, without control measures. Genotype and genotype × environment biplots and correlation analysis indicated that the significant G × E observed was not due to changes in hybrid ranking, implying absence of a significant crossover interaction. Therefore, predominance of additive gene effects imply that breeding progress for GLS disease resistance would be made through selection and this could be achieved at a few hot-spot sites, such as Baynesfield and Cedara locations in South Africa, and still deploy the resistant germplasm to other environments in which they are adapted. © 2011 Springer Science+Business Media B.V. Source


Sibiya J.,University of KwaZulu - Natal | Tongoona P.,University of KwaZulu - Natal | Derera J.,University of KwaZulu - Natal | van Rij N.,Crop Protection | Makanda I.,University of KwaZulu - Natal
Field Crops Research | Year: 2011

Phaeosphaeria leaf spot (PLS) disease (causal agent Phaeosphaeria maydis (Henn.) Rane, Payak & Renfro) of maize is increasing in importance in sub-Saharan Africa (SSA). However, there is still limited information on the combining ability for disease resistance of the germplasm that are adapted to African environments. Evaluating combining ability effects and their interactions with the environment would provide valuable information that can be used in the development of cultivars that are resistant to PLS. This study was therefore conducted to determine the combining ability, gene action and the relationship between grain yield and PLS disease severity among selected tropical advanced maize inbred lines. Forty five F1 hybrids were generated by crossing 10 inbred lines in a half diallel mating scheme. The 45 hybrids along with the ten inbred parents were evaluated in four environments, with two replications each between 2007 and 2009. General and specific combining ability (GCA and SCA) effects were highly significant (P≤0.001) for PLS, grain yield and days to anthesis. GCA effects accounted for 66-90% and SCA effects for 10-34% of the variation in the hybrids for PLS resistance, grain yield and days to anthesis. This indicated predominance of additive over non-additive gene action for the three traits in these inbred lines. The resistant inbred lines to PLS were A1220-4, N3-2-3-3, CML312, MP18 and CML488. These lines had good combining ability for PLS resistance and contributed towards resistance in their crosses. In general, resistant hybrids involved a susceptible and a resistant parent, where at least one of the parents had a negative GCA effect. In addition, lines A1220-4 and CML312 contributed towards high yield and were late maturing. Inbred line CZL00009 conferred genes for early maturity. Linear regression analysis indicated that grain yield of maize was suppressed by about 250kgha-1 per each increase in PLS disease severity score, underscoring the need to control the disease. Significant (P<0.01), negative correlations (r=-0.29 to -0.43) between grain yield and PLS severity were also detected. This showed the potential of PLS to reduce yield when favourable conditions for disease development are present. By and large, highly significant additive gene action implied that progress would be made through selection. Although non-additive effects were small (±10%), observation of dominance effects which were associated with reduced disease levels in some hybrids may be exploited in developing single cross maize hybrids among these inbreds when one parent is resistant. © 2010 Elsevier B.V. Source


Boix-Ruiz A.,University of Almeria | Galvez-Paton L.,Technical University of Madrid | de Cara-Garcia M.,Crop Protection | Palmero-Llamas D.,Technical University of Madrid | And 2 more authors.
Phytoparasitica | Year: 2015

Two Fusarium oxysporum f. sp. lycopersici (Fol race 2 and Fol race 3) and two f. sp. radicis-lycopersici (Forl) isolates plus eight to ten monosporic descendants from each were identified through molecular analysis and pathogenicity tests using differential varieties under different thermal conditions. The results for molecular and pathogenicity test for Fol were variable and to some extent contradictory. The Fol race 3 isolate and its progeny were amplified by the primers SIX1 and SIX3b but, depending on the test temperatures, the parental plus two descendants lost virulence, and one isolate completely lost virulence in all the tests. The Fol race 2 isolate was amplified by the SIX1 primer, but two descendants were not. The monosporic isolates and the parentals did not show pathogenicity on plants. All Forl isolates and progenies were amplified by the Forl primer, but one of the parentals plus all of its descendants did not show pathogenicity on plants. In addition, temperatures influenced the pathogenicity tests, yielding different virulences for Fol, which was enhanced at higher temperatures, whereas on the contrary a lower temperature was preferable for Forl. © 2014, Springer Science+Business Media Dordrecht. Source


News Article
Site: http://phys.org/biology-news/

In conjunction with plastic mulch, abrasive weeding reduced final weed biomass by 69 to 97 percent compared to non-weeded control plots, said U of I agroecologist Samuel Wortman. Abrasive weeding involves blasting weed seedlings with tiny fragments of organic grit, using an air compressor. For the current study, grit was applied through a hand-held siphon-fed sand-blasting unit connected to a gas-powered air compressor, which was hauled down crop rows with a walk-behind tractor. The study looked at a number of grit sources: walnut shells, granulated maize cob, greensand, and soybean meal. If applied at the right plant growth stage, the force of the abrasive grit severely damages stems and leaves of weed seedlings. Wortman found no significant differences between the grit types in terms of efficacy. "When it leaves the nozzle, it's at least Mach 1 [767 mph]," Wortman noted. "The stuff comes out so fast, it doesn't really matter what the shape of the particle is." Because ricocheting particles can pose a risk to the applicator, Wortman advises using protective eyewear. Blasted grit does not discriminate between weed and crop seedlings, which makes it important to use this method in transplanted crops that are substantially larger than weed seedlings at the time of grit application. Although some visible damage occurred on stems and leaves of both tomato and pepper crops, the damage did not affect marketable fruit yield. Studies are ongoing to determine whether abrasions on crop tissues could result in increased susceptibility to disease, but early results show little effect. Importantly, plots with plastic mulch and one or more blasting treatment achieved the same fruit yields seen in hand-weeded plots, and 33 to 44 percent greater yields than in non-weeded control plots. An additional benefit of weed blasting is the potential for growers to use organic fertilizers, such as soybean meal, as blasting material. "We expect that abrasive weeding could contribute between 35 and 105 kg nitrogen per hectare [31 - 94 lbs per acre] to soil fertility." The idea that a grower could both fertilize and kill weeds in a single pass is appealing, but it is still unknown whether the fertilizer would be available for plant uptake within critical windows. According to Wortman's research, weed blasting does affect some weeds more than others. Essentially, the smaller the seedling, the better. Also, seedlings whose growing points are aboveground (annual broadleaf species) are more susceptible to blasting than seedlings whose growing tips are located belowground (grasses and broadleaf perennials). Finally, Wortman noted that the presence of plastic mulch seemed to factor strongly into the equation. Weed blasting alone "is not a silver bullet, but it is an improvement," he said. The method is now being tested in different horticultural crops, including broccoli and kale, with and without additional weed control methods. Early results suggest that the presence of polyethylene mulch or biodegradable plastic mulch strongly enhances the success of weed blasting, as compared with straw mulch and bare soil. Wortman and his collaborators have also developed a mechanized grit applicator, which they are currently testing. Explore further: Biodegradable mulch films on the horizon More information: Sam E. Wortman. Air-propelled abrasive grits reduce weed abundance and increase yields in organic vegetable production, Crop Protection (2015). DOI: 10.1016/j.cropro.2015.08.001

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