Sources of resistance in wheat to speckled leaf blotch caused by Septoria tritici

Summary Seven and a half thousand wheat varieties, including over 2,000 durums, were screened for resistance to Septoria tritici under conditions of artificial inoculation in the field. From this screening, 460 varieties were selected on the basis of resistance and earliness and were subject to more detailed observation.Selected varieties were tested in the field with two replications under both natural and artificial epidemic conditions. The agreement between varietal scores in the two replications and under the two conditions was good; 91–94% of varieties showing consistent disease scores. The correlation coefficient between varietal scores for the natural epidemic and the artificial epidemic conditions was 0.63^***.A number of the very early maturing varieties of T. aestivum showed good resistance as measured by pycnidial production but exhibited extensive leaf necrosis. This reaction was not observed in later varieties and in accessions of T. durum.Varieties of Triticum durum were typically more resistant than varieties of T. aestivum. Thirty-four varieties of T. aestivum and 266 varieties of t. durum showed a consistent expression of resistance. A list of these 34 accessions of T. aestivum and selected accessions of T. durum is provided, along with agronomic data.     

Persistence and colonization of gaps in sown swards of grass and clover under different sward managements

The effects of extensive sward management and patch size on the persistence and colonization of gaps in sown swards was examined by creating gaps of five different sizes (2·3, 7, 10, 14 and 19 cm in diameter) in four different sward treatments: a fertilized sward grazed to 4 cm, i.e. relatively intensive management, and three extensively managed unfertilized swards, which were not grazed or grazed to 4 cm or 8 cm. The swards were originally sown with ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.), but had developed differences in species composition as a result of the management treatments imposed 2 years before and during the experiment. Light quality measurements, i.e. red-far red (R/FR) ratio, were used to determine when the light environment in the gaps no longer differed from that in control, uncut patches and this was used as an estimate of gap persistence. Persistence of gaps depended on both sward management and gap size. Gaps disappeared most rapidly in the ungrazed sward and fertilized 4-cm sward, and most slowly in the unfertilized 8-cm sward. Small gaps persisted for up to 2 weeks in all but 8-cm swards, whereas larger gaps were estimated to persist for up to 20–25 weeks in unfertilized, grazed swards. There was no evidence that the number of grass or dicotyledonous species increased in the gaps compared with the control areas. There were significant positive linear relationships between the vegetation that developed in gaps and that in the control, uncut patches, reflecting the different species composition of the established sward of the grazed (grass-dominant) and ungrazed (Ranunculus repens-dominant) treatments. For total grass dry matter and tiller numbers, as well as L. perenne tiller numbers, there was a small, but significant, effect of both patch size and sward management on the slopes of the regressions between the controls and gaps. The results are discussed in relation to the potential for species composition of sown swards to change as a result of gap creation.     

Genetic improvement of the Pacific oyster Crassostrea gigas (Thunberg) in Australia

The Pacific oyster industry in Australia is derived from importations from Japan in the late 1940s and early 1950s to Tasmania and is almost completely hatchery based. This makes it a good target for developing and deploying genetically improved strains. An allozyme survey comparing hatchery stocks with self‐recruiting Tasmanian stocks and with two collections from Japan found abundant variation and no significant evidence of allele loss. The subsequent selection programme (initiated in the summer of 1996/97) had several strands. We wanted to take advantage of the increased power that marker‐assisted selection could bring and, therefore, needed to develop a linkage map and isolate flanking markers around quantitative trait loci (QTLs). Several types of markers (allozymes, microsatellites and AFLPs) were used, and single‐pair crosses were set up; QTLs have been detected. Conventional selection programmes, one based on mass selection and one on family selection, have been established. Triploid Pacific oysters produced via chemical means have been available for several years, but rates of triploidy achieved by such means are usually less than 100%. In 1999, we will assess whether our tetraploid 2‐year‐old broodstock can be crossed with diploids to give 100% triploid offspring.     

Anthropogenic effects on soil quality of ancient agricultural systems of the American Southwest

Soil studies of ancient agricultural fields contribute to research on long-term human–environmental relationships and land use sustainability. This kind of research is especially applicable in desert landscapes of the American Southwest because: (1) soil formation is slow enough that cultivation effects persist for centuries to millennia; (2) many ancient fields in valley margins have remained uncultivated since they were abandoned, so long-term soil properties reflect ancient agricultural use; and (3) agricultural features (e.g., terraces, rock alignments and rock piles, and irrigation canals) provide clues for identifying and sampling ancient cultivated and uncultivated soils. Surficial remnants of these field systems persist and remain intact in many cases. Soil studies of ancient and modern American Indian agricultural systems across the Southwest indicate that soil changes are highly variable, ranging from degradation (e.g., organic matter/nutrient decline, compaction), to minimal net change, to enhanced soil quality. Soil changes caused by cultivation can be inferred by comparing soils in agricultural fields relative to reference uncultivated areas in similar landscape settings (that is, space-for-time substitution). Soil response trajectories vary for a number of reasons, such as variability in initial ecosystem conditions, diversity in agricultural methods, variability in the mix of crops and cropping intensity, and environmental sensitivity to alteration (varying resistance and resilience). Studies of rock mulch soils indicate enhanced fertility, with elevated organic carbon, nitrogen, and available phosphorus levels, increased infiltration rates and moisture retention, and no evidence of compaction. By contrast, cultivation effects vary widely for terraced soils. Although numerous studies have focused on irrigation canals, irrigated soils have received far less attention. Soil studies of irrigation systems along the Gila and Santa Cruz rivers of Arizona now underway will help fill this research gap.     

Effect of Steeping Conditions on Wet-Milling Characteristics of Hard Red Winter Wheat

A batch-wise small-scale wet-processing laboratory for whole wheat kernel has been designed and constructed to produce wheat starch and gluten from wheat grains. Hard red winter wheat kernels were steeped in three steeping media: SO₂ solution, lactic acid, and hydrochloric acid. Acid concentrations of 0.1, 0.3, and 0.5%, were used for SO₂ solutions and hydrochloric acid, and 0.1, 0.6, and 3.0% for lactic acid. After 16, 20, and 24 hr of steeping, the wheat was wet-milled. Yields and protein contents of wet-milling fractions were compared. Both high concentration of steeping media and long steeping time increased the starch yield and decreased the protein contents of the starch. However, the steeping time and acid concentration could be reduced from 24 to 20 hr and from 0.5 to 0.3%, respectively, without any statistically significant difference in starch yields or protein contents of the starch. Consistency and color of the starch were affected by both steeping time and acid concentrations of steeping media.     

Participation of specific PKC isozymes in the inhibitory effect of ET-1 on progesterone accumulation in cells isolated from early- and mid-phase corpora lutea

Expression of PKC alpha, beta I, beta II, epsilon and micro has been demonstrated in the whole bovine CL with PKC epsilon being differentially expressed as a function of development. In experiment 1 we have investigated the amount of mRNA encoding PKC epsilon at different stages of luteal development (days 1, 4, 10 and 17). In experiment 2, the cellular source of luteal PKC isozymes was determined. Enriched steroidogenic (SC) and endothelial (EC) cells from day-10 CL were used to examine this question by Western blot analysis and immuno-histochemistry. In experiment 3, Western blot analysis was used to examine the ability of ET-1 to activate luteal PKC isozymes in day-10 CL. In experiment 4, the role of luteal PKC isozymes in the ET-1 mediated inhibition of P(4) accumulation in steroidogenic cell cultures from day-4 and day-10 CL was examined. Abundance of PKC epsilon mRNA gradually increased from day-1 to -10 with no further increase on day-17. In experiment 2, PKC epsilon was exclusively detected in SC (LLC and SLC). In contrast, PKC alpha, beta I and beta II were detected in both SC and EC, with EC expressing higher amounts of PKC isozymes. In day-10 CL, ET-1 induced cellular redistribution of PKC alpha, beta I, epsilon but not beta II. Inhibitors specific for conventional PKC isozymes as well as PKC epsilon were able to negate the inhibitory effects of ET-1 on P4 accumulation in the day 10 CL. In the day-4 CL, the inhibitory effect of ET-1 might be mediated via conventional PKC. Thus, an exclusive presence of PKC epsilon in luteal steroidogenic cells, its higher expression along with the ability of ET-1 to stimulate its activation in day-10 CL strongly suggests that this PKC isoform may play an important regulatory role in decreasing P(4) during luteal regression. Inhibition of P(4) by ET-1 in the early CL may be mediated via conventional PKC isozymes.     

Evaluation of upper respiratory tract function during strenuous exercise in racehorses

Forty-six racehorses with a history of poor performance underwent endoscopic evaluation of laryngeal and pharyngeal function while exercising on a high-speed treadmill. This evaluation allowed the definitive diagnosis of intermittent or continual upper respiratory tract obstruction as a cause of poor performance, as well as the documentation of the dynamic functional anatomy of the obstruction. Ten of the horses (22%) were determined to have a functional abnormality of the upper respiratory tract. These abnormalities included epiglottic entrapment (1 horse), persistent dorsal displacement of the soft palate during exercise (4 horses), and left laryngeal hemiplegia (5 horses). Thirty-two horses were observed to have signs of left laryngeal hemiparesis (asynchronous arytenoid movement) at rest that did not impair full laryngeal abduction during strenuous exercise.