Evaluation of herbicides for selective weed control in grafted watermelons

Grafted watermelon is a combination of two plants, aCucurbita rootstock and a watermelon scion. Therefore, weed control for this crop faces a unique problem: the safety of the selected herbicide has to be tested for both plants that make up the grafted plant. In the current study, we evaluated the usage safety of selected herbicides forCucurbita rootstocks as well as for non-grafted and grafted watermelons, and the control ofAmaranthus retroflexus by the same herbicides. In addition, the residual effect of the herbicides was tested for seeded and transplanted melons representing the next crop following cultivation of the grafted watermelons. The herbicides ethalfluralin, pendimethalin, ethalfluralin, sulfentrazone, oxyfluorfen, chlorsulfuron and clomazone were chosen for their potential to controlA. retroflexus. Pendimethalin and trifluralin were less effective than the other herbicides in controllingA. retroflexus; sulfentrazone, chlorsulfuron and clomazone were not safe for use on the tested cucurbits and thus cannot be recommended for weed control in grafted watermelons. Therefore, by eliminating the herbicides that are toxic to cucurbits and those that are ineffective forA. retroflexus control, it was concluded that the herbicides ethalfluralin and oxyfluorfen can be considered effective and safe for weed control in grafted watermelons. It was shown that trifluralin and oxyfluorfen have the potential to be applied effectively through the drip irrigation system. http://www.phytoparasitica.org posting Jan. 10, 2008.     

Peat in the inoculation medium induces fusarium susceptibility in melons

The effect of peat moss on fusarium wilt of melon ( Cucumis melo L.) was studied in order to improve the selection process of resistant melons during breeding programmes. Disease symptoms were evident earlier and disease progress was faster in seedlings that were transplanted to peat following inoculation than in those transplanted to sand. The resistant breeding line used as a control did not show any wilt symptoms in either medium. Mixing the peat with sand or perlite reduced the disease development rate and the final disease incidence. The effects of peat and sand on disease progress were evaluated with two segregating melon populations in which the expected susceptible : resistant ratio was 25 : 75. In both populations, disease incidence was higher in the peat, which enables breeders to identify resistant plants and to lower the risk of using escapees as resistant plants. The mechanism of disease enhancement may include both biotic and abiotic components. There is an indication that peat induces plant susceptibility before inoculation. Melon seedlings germinated in peat and transplanted into sand exhibited significantly greater wilt incidence than those that germinated in sand and were transplanted into sand following the inoculation. Disease progress in sterile peat was significantly slower than that in non-sterile peat, which suggests the possible involvement of microbial activity.     

The efficacy of ultrasonic fumigation for disinfestation of storage facilities against postharvest pathogens

Inoculum of postharvest pathogens can accumulate inside storage rooms and contaminate new batches of fruit and vegetables, but this chain can be broken by disinfecting storage facilities between storage periods. Quaternary ammonium (QA) has been known for over 50 years as an efficient disinfectant against microorganisms, with wide applications in the food industry. The aim of this study was to determine the efficacy of didecyldimethylammonium chloride (Sporekill, designated here as QA^sk), against development of Botrytis cinerea after direct exposure or by ultrasonic fogging. Following direct exposure to a concentration of QA^sk below 5 mg L^?1, a population of 10⁴ conidia of B. cinerea was inactivated after 2 min; ultrasonic fogging with QA^sk at 500 mg L^?1 took 30 min to achieve consistent inactivation. Fumigation at 20 °C was considerably more effective than fumigation at 5 °C, and similar results were obtained for three other postharvest pathogens, Penicillium expansum, Colletotrichum gloeosporioides and Alternaria alternata. These results show that conidia of B. cinerea are highly sensitive to direct exposure to QA^sk, but that effective sanitation of a storage facility by ultrasonic fumigation requires a QA^sk concentration two orders of magnitude greater.     

Reduction of postharvest losses of Galia melon by a short hot-water rinse

A rapid method for simultaneously rinsing and disinfecting fresh harvested produce using a hot-water rinse and brushes (HWRB) was tested on Galia melon ( Cucumis melo cv. reticulatus ) fruit. The optimal treatment to reduce decay while maintaining fruit quality after prolonged storage and marketing simulation was 59 ± 1°C for 15 s. Trial shipments by sea transport to Europe demonstrated that treating melon with a commercial-scale HWRB machine (3 tonnes fruit h⁻¹) maintained significantly better overall quality of treated fruit compared with untreated fruit. Exposing spores of Alternaria alternata and Fusarium solani to 60°C for about 15 s in vitro reduced germination by 48% and 42%, respectively. Employing HWRB resulted in a 3-log reduction in total colony-forming units (CFU) of the epiphytic microbial population, compared with untreated fruit. Scanning electron microscopy (SEM) showed that HWRB removed soil, dust and fungal spores from the fruit surface, and partially or entirely sealed natural openings in the epidermis.     

Assessing the effect of genetic and anatomic variation of Cucurbita rootstocks on vigour,survival and yield of grafted melons

Summary

Melon (Cucumis melo L.) ‘Arava’ was grafted onto 22 experimental Cucurbita rootstocks including intra- or interspecific hybrids to examine scion-rootstock compatibility and to correlate plant performance under greenhouse and field conditions. The commercial Cucurbita ‘TZ-148’ rootstock and non-grafted plants were used as controls. Numbers of leaves, stem length and plant fresh weights were recorded three weeks after planting. Vegetative growth of the grafted plants varied markedly, indicating differences in compatibility between the scion and rootstocks. A positive correlation was found between number of leaves, stem length and fresh weight of melon plants. No significant advantage in vegetative growth was found in melons grafted onto intra- or interspecific hybrid rootstocks. Stem diameter and number of vascular bundles of the rootstock did not correlate with scion plant fresh weight. Twelve selected rootstocks out of the 22 tested were grown in the field during the spring and autumn, to determine if there is an association between the plant performance in the greenhouse and fruit yield under field conditions. Positive and significant correlations were found between greenhouse growth parameters and fruit yield under field conditions. It is suggested that testing grafted melons under greenhouse conditions could be a useful tool for preliminary testing of scion-rootstock compatibility.     

Induction of Resistance to Penicillium digitatum in Grapefruit by β-Aminobutyric Acid

-Aminobutyric acid (BABA), an inducer of pathogen resistance in plants, induced disease resistance in reproductive parts of the plant, such as grapefruit peel tissue. Application of BABA to specific wound sites on the fruit peel surface induced resistance to Penicillium digitatum, the main postharvest pathogen of citrus fruit, in a concentration-dependent manner, being most effective at 20mM, and rather less effective at either higher or lower concentrations. The effect of BABA in inducing resistance to P. digitatum in the fruit peel surface was local and limited to the vicinity (within 1–2cm) of the BABA-treated site. In addition to inducing pathogen resistance, increasing concentrations of BABA (from 1 to 100mM) also exhibited direct antifungal activity and inhibited P. digitatum spore germination and germ tube elongation in vitro. The induction of resistance to P. digitatum by BABA was accompanied by the activation of various pathogen defense responses in grapefruit peel tissue, including activation of chitinase gene expression and protein accumulation after 48h, and an increase in phenylalanine ammonia lyase (PAL) activity after 72h.