Hybridization barriers between diploid Solanum tuberosum and wild Solanum raphanifolium

Wild potato germplasm represents a unique, diverse and accessible resource for disease and pest resistance, along with useful agronomic traits that may be introgressed into the cultivated potato (Solanum tuberosum L.). Hybridization of diploid wild Solanum species with haploids (2×) of cultivated potato (4×) is generally an effective technique for introducing genetic diversity and desirable traits into potato. However, in this study, hybridization barriers were found in crosses between S. tuberosum haploids and the wild species S. raphanifolium. Male sterility, likely due to nuclear-cytoplasmic interactions, was observed in some haploid tbr?×?S. raphanifolium hybrids. In addition, pollen-pistil incompatibilities were observed in backcross, F2, and reciprocal cross hybridization attempts that failed to produce seed. More crosses were successful when F1 clones were crossed as females to wild clones than to cultivated clones. When crosses were made in the other direction, with F1 hybrids used as male parents, seeds were almost never produced.     

THE DISTRIBUTION OF LEAF AREA AND LIGHT INTENSITY WITHIN WHEAT CROPS DIFFERING IN ROW DIRECTION, ROW SPACING AND RATE OF SOWING; A CONTRIBUTION TO THE STUDY OF UNDERSOWING PASTURE WITH CEREALS

The distribution of leaf area and light intensity within wheat crops differing in row direction, row spacing and rate of sowing is described. Regardless of the manner of planting, 75% of the total leaf area was found within a band 31/2 in. wide, centred on the centre of the row. Light penetration within crops spaced at 14 in. was greater than within those spaced at 7 in. Light penetration within rows running N.–S. was more uniform and higher, particularly around noon, than within rows running E.-W. Within N.-S. rows the position midway between rows received the highest amount of light, but light decreased on either side until it was least beneath the rows. Within E.-W. rows at 14 in. spacing, maximum light was recorded at 101/2 in. on the southern side of a row, decreasing progressively as the row was approached.     

Cotyledon angle as a predictor of growth rate of cucumber plant

Summary Experiments conducted in the greenhouse and in the field indicated that plants produced from seedlings of Cucumis sativus L. which displayed their cotyledons in an upward position grew faster than plants which displayed their cotyledons in a downward position. Cotyledon angle was not a function of seed size nor seedling weight at 10 days after planting. An increase in plant height, node number, and fresh weight at later growth stages was associated with an upward cotyledon angle and persisted until time of harvest. Anthesis tended to occur later in plants having a downward cotyledon angle. The number of pistillate flowers was greater in plants with an upward cotyledon angle compared to those with a downward cotyledon angle. Differences in yield (fruit number) were not associated with cotyledon angle.Paper No. 5432 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, NC. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Experiment Station of products named, nor criticism of similar ones not mentioned.     

Phoma stem canker (<Emphasis Type="Italic">Leptosphaeria maculans/L. biglobosa</Emphasis>) of oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis>): is the G<Subscript>2</Subscript> Disease Index a good indicator of the distribution of observed canker severities?

Several disease indices (DI) have been proposed to assess the severity of phoma stem canker at late growth stages. The DI commonly used in France (called G₂ DI) consists of integrating the distribution of the proportions of plants observed within six canker severity classes into a single index. This index uses arbitrarily chosen coefficients associated to each class of canker severity. A given value of this DI can therefore be obtained with different distributions among the canker severity classes. Consequently, it is important to assess to what extent the G₂ DI is representative of the distribution of plants in canker severity classes. We show in this study that the G₂ DI is a good indicator of the distribution of the observed canker severities, using a dataset from different years, sites and cultivars; this illustrates the robustness of the G₂ DI.     

Seasonality of Eurytoma sp.—a parasitoid on okra petiole maggot,Melanagromyza hibisci Spencer

Abstract

Studies on the seasonal abundance of Eurytoma sp. a parasitoid on okra petiole maggot, Melanagromyza hibisci Spencer were conducted for one year. Per cent parasitism ranged from 10 to 68 during the study period. However, there was no significant relationship between percentage parasitism on host density. Data further revealed that parasitoid response to host density was weak.     

Two perennial legumes (Astragalus adsurgens Pall. and Lespedeza davurica S.) adapted to semiarid environments are not as productive as lucerne (Medicago sativa L.), but use less water

Perennial forage legumes, particularly lucerne (Medicago sativa L.), play a significant role in crop/livestock mixed farming systems in the semiarid region of the Loess Plateau of China as stock feed and a source of nitrogen for subsequent crops. However, there is evidence that lucerne reduces soil water deep in the soil profile, thereby reducing subsequent crop productivity. From 2004 to 2010, this study evaluated the forage productivity and water use of two locally adapted perennial legume species, milk vetch (Astragalus adsurgens Pall.) and bush clover (Lespedeza davurica S.), compared with lucerne. The 7‐year total and average annual forage yield of milk vetch were 56 and 8 t ha^?1 and bush clover was 42 and 6 t ha^?1, respectively, significantly lower than lucerne at 91 and 13 t ha^?1. However, despite lower water‐use efficiencies (16 and 12 kg ha^?1 mm^?1 for milk vetch and bush clover, respectively, compared to 22 kg ha^?1 mm^?1 for lucerne), the total 7‐year water use in milk vetch and bush clover was 3500 mm and 3490 mm, respectively, which was 135–140 mm less than lucerne. After 7 years, lucerne had extracted water from the upper 5 m soil, whereas bush clover used water mainly from the upper 2 m of the soil profile and milk vetch still had some water available below 3 m. We conclude that while the locally adapted forage legumes were not as productive as lucerne as a source of fodder in mixed cropping/livestock system in this region, they use less water, which may be advantageous in drier regions.     

The nutritional value of pressed potato vine silage

Potato (Solanum tuberoswn L.) vines were studied to determine if they could be successfully ensiled and fed to ruminant animals. Russet Burbank potato vine and alfalfa (Medicago sativa L.) silages were fed to goats (Capra hircus) to measure in vivo digestibility and to determine if potato glycoalkaloids were aversive or toxic. No differences in the feeding patterns between control and experimental animals were observed. Alfalfa silage was more digestible than the Russet Burbank potato vine silage due to a higher content of digestible cell wall materials. Digestibility differences between potato clones and harvest dates were found when in vivo digestibility tests were performed. W729R was the most digestible clone studied, especially for the early harvest dates. Most of the clones had vines that were more digestible, in vitro, than alfalfa. Vine glycoalkaloid contents of the experimental clones were similar to the values reported in the literature. There was no apparent correlation between vine glycoalkaloid content and percent digestible dry matter. A positive correlation of 0.38 between digestible dry matter and dry vine yield was found. Potato vine silage, produced after pressing the vines to remove water, was an acceptable feed for ruminant animals. Additional in vivo testing is necessary to determine if toxic effects due to glycoalkaloids or pesticides from long term feeding will be a problem.     

Rectificatie

An erratum to this article is available at .     

Relative importance of seed‐tuber and soilborne inoculum in causing black dot disease of potato

Controlled‐environment and field experiments were done to quantify the individual contribution of seed‐tuber and soilborne inoculum of Colletotrichum coccodes in causing black dot disease of potato tubers. Seed‐tuber and soilborne inocula of C. coccodes were quantified using an existing real‐time PCR assay and related to subsequent incidence and severity of disease. In four field trials, a controlled‐environment experiment and through the monitoring of 122 commercial crops, seed‐tuber inoculum was found to be relatively less important than soilborne inoculum in causing black dot, and the level of seed‐tuber inoculum did not significantly affect either the incidence or severity of disease or the percentage of progeny tubers deemed unmarketable. By contrast, soilborne inoculum had the potential to result in high levels of disease and the level of C. coccodes soil infestation (pg DNA g^?1 soil) was found to have a significant effect. At soil infestation levels below 100 pg DNA C. coccodes g^?1 soil, 7% of commercial crops had an incidence of black dot greater than 20%, increasing to 40% and 57% of crops at levels of 100–1000 pg g^?1 and >1000 pg g^?1 soil, respectively. These arbitrary threshold levels for soilborne inoculum related to disease risk are discussed. Interpretation of disease risk based on inoculum levels must, in the future, be informed by agronomic variables and potential control strategies.