Epiphytic yeasts, which colonize plant surfaces, may possess activity that can be harnessed to help plants defend themselves against various pathogens. Due to their unique characteristics, epiphytic yeasts belonging to the genus Pseudozyma hold great potential for use as biocontrol agents. We identified a unique, biologically active isolate of the epiphytic yeast Pseudozyma aphidis that is capable of inhibiting Botrytis cinerea via a dual mode of action, namely induced resistance and antibiosis. Here, we show that strain L12 of P. aphidis can reduce the severity of powdery mildew caused by Podosphaera xanthii on cucumber plants with an efficacy of 75%. Confocal and scanning electron microscopy analyses demonstrated P. aphidis proliferation on infected tissue and its production of long hyphae that parasitize the powdery mildew hyphae and spores as an ectoparasite. We also show that crude extract of P. aphidis metabolites can inhibit P. xanthii spore germination in planta. Our results suggest that in addition to its antibiosis as mode of action, P. aphidis may also act as an ectoparasite on P. xanthii. These results indicate that P. aphidis strain L12 has the potential to control powdery mildew.

The efiects of 10, 12.8, 18.3, and 26.7 Ctem-marily to poor pollen viability and germinaperatures on flower production, fruit-set and tion, and to a lesser extent to high stigrna size, pollen viabilityf stigma receptivity, and position in the antheridial cone. Et ZA.1 C, the height of stigma in the antheridial cone the high level of the stigma in the antheridial was determined in tomato lines selected for cone was the main factor reducing fruit-set abilitv_to.set fruit at high or 1ow temperatures. but the low stigma receptivity was a factor in Low fruit-set at 10

The dynamics of hydrogen peroxide (H(2)O(2)) was investigated from December 2007 to October 2008 in the Gulf of Aqaba, which in the absence of H(2)O(2) contribution from biological production, rain and runoff, turned out to be a unique natural photochemical laboratory. A distinct seasonal pattern emerged, with highest midday surface H(2)O(2) concentrations in spring-summer (30-90 nM) as compared to winter (10-30 nM). Similarly, irradiation normalized net H(2)O(2) formation rates obtained in concurrent ship-board experiments were faster in spring-summer than in winter. These seasonal patterns were attributed to changes in water characteristics, namely elevated spring-summer chromophoric dissolved organic matter (CDOM). The role of trace elements in H(2)O(2) photoformation was studied by simultaneously measuring superoxide (O(2)(-)), Fe(II), and H(2)O(2) formation and loss in ambient seawater and in the presence of superoxide dismutase, iron and copper. O(2)(-) was found to decay fast in the Gulf water, with a half-life of 15-28 s, primarily due to catalytic reactions with trace metals (predominantly copper). Hence, H(2)O(2) formation in the Gulf involves metal-catalyzed O(2)(-) disproptionation. Added iron moderately lowered net H(2)O(2) photoformation, probably due to its participation in Fe(II) oxidation, a process that may also modify H(2)O(2) formation in situ.

Two populations of corn (Zea mays L.) improved by nine cycles of mass selection for yield and the unselected parent variety, ‘Hays Golden,’ were evaluated in 1969 and 1970 using random S1 lines and their testcrosses to related and unrelated single‐cross testers. One selected population received thermal neutron seed treatment prior to the first and third selection cycles.S1 lines of the selected populations, per se and in testcrosses, demonstrated significant superiority in mean yield over lines of the parent variety in each year. Like progenies of the two selected populations produced similar yields. Selection evidently eliminated radiation‐induced deleterious mutants from the “irradiated” population while increasing frequencies of favorable yield genes common to both selected populations. This apparently produced similar germ plasm reservoirs much more suitable for the extraction of superior inbred lines than the parent variety. Indications are that selection also reduced genetic variability in yield and combining ability.Prolificacy resulting from selection for yield was evident in S1 lines but not in the testcrosses. Since inbreeding did not reduce prolificacy in the selected populations, results are interpreted to mean that tester genes masked recessive genes which induce prolific potential when homozygous. All phenotypic correlations between S1 and testcross yields were too low to be of much predictive value; but in general, lines of the selected populations exhibited the least correlation with their testcrosses. Genetic correlations were somewhat higher, indicating sizeable environmental fluctuations in individual experiments. We postulate that non‐prolific testers by inhibiting prolificacy in turn limit the expression of genes controlling yield in these populations. Use of a prolific tester might have provided greater yield differentiation, more precise estimates of line genotypes and higher correlations between S1 and testcross progenies.

Summary Many types of yeast have been studied in the last few years as potential biocontrol agents against different phytopathogenic fungi. Their ability to control plant diseases is mainly through combined modes of action. Among them, antibiosis, competition for nutrients and niches, induction of systemic resistance in plants and mycoparasitism have been the most studied. In previous work, we have established that the epiphytic yeast Pseudozyma aphidis inhibits Botrytis cinerea through induced resistance and antibiosis. Here, we demonstrate that P. aphidis adheres to B. cinerea hyphae and competes with them for nutrients. We further show that the secreted antifungal compounds activate the production of reactive oxygen species and programmed cell death in B. cinerea mycelium. Finally, P. aphidis and its secreted compounds negatively affect B. cinerea hyphae, leading to morphological alterations, including hyphal curliness, vacuolization and branching, which presumably affects the colonization ability and infectivity of B. cinerea . This study demonstrates additional modes of action for P. aphidis and its antifungal compounds against the plant pathogen B. cinerea .