Factors affecting the development of populations of Oxalis pes-caprae L.

As the control of Oxalis pes-caprae L. is dependent upon treatment after the parent bulb has become exhausted and before the new bulbs have formed, experiments were conducted to test the uniformity of development of plants and to determine if adequate control could be expected from a single herbicide application. Inherent differences were observed in the time of emergence, and further differences could be induced by increasing the depth of planting or withholding water. Competition between plants was shown to retard the development of late-emerging plants. The physical removal of parts of the plant before bulb exhaustion had limited effect on bulb production, but reduced bulb weights and numbers when carried out after bulb exhaustion. Although not all parts of the plant were replaced by regrowth, no major changes in overall development were noted.     

Effect of selection for pseudo-self compatibility in advanced inbred generations of Nemesia strumosa Benth.

Summary Highly pseudo-self compatible (PSC) Nemesia strumosa plants were selfed and intercrossed to produce progenies of the F₅ through F₇ generations. Though high PSC progenies were obtained, none were truebreeding. Progenies from crossing inbred high PSC plants to low PSC plants consisted of either mostly low PSC plants or both low and intermediate plants. A backcross to the high PSC parent of a progeny from a low times high cross produced a family with a PSC frequency distribution skewed toward low PSC but with a few high PSC plants. These data may be explained if PSC genes at some or most loci are incompletely dominant to non-PSC genes and threshold numbers of PSC genes are required for PSC expression and for 100% PSC plants. Dominance may also occur at some loci. Although only a small number of genes may be required to produce a high PSC plant, the total number of PSC genes may be large.Scientific Journal Series Paper No. 11,676 of the Minnesota Agricultural Experiment Station.     

Evaluation of Infection Processes and Resulting Disease Caused by Dendryphion penicillatum and Pleospora papaveracea on Papaver somniferum

ABSTRACT Two pathogenic fungi of opium poppy, Pleospora papaveracea and Dendryphion penicillatum, were isolated from field material in Beltsville, MD. The processes of infection by these two fungi were studied to determine the optimal environmental conditions for infection. Both fungi formed appressoria capable of penetrating directly through the plant epidermal layer. Of the two fungi, P. papaveracea was more aggressive, causing more rapid necrosis. Appressorial formation by P. papaveracea occurred as early as 4 h after application of a conidial suspension to poppy leaves. P. papaveracea formed more appressoria than did D. penicillatum, especially at cool temperatures (7 to 13 degrees C). In greenhouse studies, P. papaveracea caused more damage to opium poppy than did D. penicillatum when applied in 10% unrefined corn oil. In the field, P. papaveracea was more consistent in its effects on opium poppy from a local seed source designated Indian Grocery. P. papaveracea caused higher disease ratings, more stem lesions, and equal or greater yield losses than did D. penicillatum on Indian Grocery. The late-maturing opium poppy variety White Cloud was severely damaged by disease, regardless of formulation or fungal treatment. P. papaveracea was the predominant fungus isolated from poppy seed capsules and the only fungus reisolated from the field the following year. These studies provide a better understanding of the infection process and the differences between these two pathogenic fungi and will be beneficial for the development of the fungi as biological control agents.     

Variation of flowering time in inbred brussels sprouts and cabbage (Brassica oleracea L.)

Summary Differences in time of flowering between two parent lines of F₁ varieties of Brassica oleracea could significantly affect both the total seed yield and the proportion of sibs in the hybrid seed crop.The results for the time to flower of an incomplete diallel show that even in relatively inbred material of brussels sprouts there is potential to select for altered flowering time. Results obtained from a set of highly inbred cabbage lines which were given three temperature regimes in early spring show that between line variation is complicated by different responses of some of the lines to the environments.     

Composting to sanitize plant‐based waste infected with organisms of plant health importance

The potential for using the composting process to sanitize plant waste infected with one of three plant pathogens was investigated using bench‐scale composting equipment. Two of these pathogens, the potato wart disease fungus Synchytrium endobioticum and Potato spindle tuber viroid (PSTVd) are currently subject to European quarantine regulations. The third, Polymyxa betae, a parasite of sugar beet, is regulated in some European countries when in association with Beet necrotic yellow vein virus (BNYVV), the causal organism of rhizomania disease of sugar beet. Survival of test organisms following various combinations of compost temperature, exposure time and moisture was determined using RNA‐based detection methodology and/or plant‐based bioassays. Mathematically definable relationships between compost treatment (temperature/time) and organism viability were identified for P. betae and S. endobioticum; these give some indication of the practicality of using composting for dealing with infected wastes. However, for PSTVd, the considerable variability in measured susceptibility of the viroid to the composting process meant that no such definable relationship could be determined and further work would be needed to extrapolate to practical situations.     

SSR assessment of Phytophthora infestans populations on tomato and potato in British gardens demonstrates high diversity but no evidence for host specialization

Phytophthora infestans populations can differ in composition as a result of host specialization on tomato and potato hosts. In Great Britain many amateur gardeners grow outdoor tomatoes but there is little or no commercial tomato production outdoors. This study analysed isolates of P. infestans from British gardens with 12 multiplexed simple sequence repeat markers that are used to monitor the disease on commercial potato crops. Samples of P. infestans from tomato hosts were collected in 3 years and from potato in 1 year from across Great Britain. Seven previously unreported clonal lineages were detected in garden populations and higher frequencies of unique clonal lineages (28–40%) were present compared with populations from British commercial potato crops reported elsewhere. Garden populations had a lower proportion (11–48% less) of the most common lineages (13_A2 and 6_A1) that together made up at least 86% of the commercial potato populations during the sampling period. Host species accounted for only 2·0% of molecular variance detected between garden potato‐ and tomato‐hosted samples. No significant difference in clonal lineage composition was found between host species in Great Britain and this could be due to the whole P. infestans population overwintering on potato. British garden populations on both hosts were much more diverse than those on commercial potato crops; this finding may be influenced by less frequent fungicide use by gardeners and a higher diversity of unsprayed susceptible potato cultivars, enabling metalaxyl‐sensitive and less aggressive genotypes to survive in gardens.     

Cellulose content as a selection trait in breeding for kraft pulp yield in Eucalyptus urophylla

? The aim of this study was to investigate the effectiveness of using cellulose content, measured by the diglyme-HCl method, as a selection trait in breeding programs for kraft pulp yield in Eucalyptus urophylla.

? A total of 275 trees from sixty-two families were sampled from a thinned progeny trial of E. urophylla in northern Vietnam to evaluate cellulose content from breast-height increment cores. Among those, twenty unrelated trees were felled to evaluate cellulose content and pulp yield from breast-height disk samples.

? The regression of pulp yield of disk samples on cellulose content was strong either from disks (R ² = 0.83) or increment cores (R ² = 0.69). There was no significant difference in cellulose content between the provenances. The narrow-sense within-provenance heritability of cellulose content was 0.50 and the coefficient of additive genetic variation was 3.9%. Genetic correlations between cellulose content and growth (0.28–0.45) or wood basic density (?0.02) were not significantly different from zero.

? Breast-height increment core cellulose content measured by diglyme-HCl method is under strong genetic control and can be used to rank trees for pulp yield in E. urophylla plantations. Selection for increased cellulose content would have only minor effects on growth and wood basic density.

     

Cytoplasmic relatedness of apple landraces and cultivars: a molecular analysis

Summary Mitochondrial DNA (mtDNA) diversity has been determined in apple landraces and cultivars, based upon restriction fragment length polymorphisms (RFLPs) for several mitochondrial genes. Our analysis includes three cultivars, Golden Delicious, McIntosh and Delicious, which represent the various patterns of mtDNA polymorphisms previously described (Ishikawa et al., 1992). A total of five RFLPs were detected, allowing classification of the apple genotypes into four cytoplasmic groups: GroupI, Golden Delicious-type; GroupII, McIntosh-type; GroupIII, Delicious-type; and Group IV, Dolgo Crab-type. European landraces and cultivars were assigned to Groups I, II, and III, while chinese crab apples were placed in either Group III or IV.     

Effect of Relative Humidity on Sporulation of Fusarium oxysporum in Various Formulations and Effect of Water on Spore Movement Through Soil

ABSTRACT Fusarium oxysporum f. sp. erythroxyli is being investigated as a mycoherbicide for the narcotic plant coca. Sporulation of the fungus in seven formulations containing different organic substrates and movement of its propagules through soil were studied. The formulations were a granular wheat flour/kaolin (pesta); an extruded wheat and rice flour (C-6); and five alginate pellet products containing corn cobs, soybean hull fiber, canola meal, rice flour, or rice flour plus canola oil. Formulations were incubated at 25 degrees C for 6 weeks in desiccators with various salt solutions to provide nine relative humidities (RH), ranging from 100% (pure deionized water) to 0% (anhydrous (CaSO(4)). Hyphae of F. oxysporum f. sp. erythroxyli grew out of alginate pellets with canola meal, rice, and rice plus canola oil as early as 24 h at 100% constant RH. Alginate pellets of rice plus canola oil and granular C-6 and pesta formulations consistently produced more microconidia, macroconidia, and CFU than the other four formulations at all RH tested. The C-6 formulation produced more propagules than the other formulations at low RH (<53%). Canola meal pellets produced more spores than three other formulations when exposed to fluctuating RH (100 to 75%). The effect of percolating water on spore movement through soil was studied using a plant-pathogenic isolate of F. oxysporum f. sp. niveum. To determine the effect of water percolation on propagule movement, formulations were placed on soil columns and artificial rain was applied. In general, 10-fold fewer CFU were recovered at a 8- to 10-cm depth compared with a 0- to 2-cm depth.