Factors affecting development of Septoria tritici in winter wheat and its effect on yield

Severe infection with Septoria tritici occurred in four of five experiments designed to create a series of different disease epidemics. These experiments successfully identified periods suitable for infection. They also indicated the effect of sprays, timed before and after these periods, on disease development and yield.
Analysis of disease progress and weather records suggested that critical conditions for initial development of S. tritici occurred during early May at four sites. Heavy rain giving at least 10 mm on 1 day or a total of 10 mm or more on 2 or 3 successive days occurred at all four sites prior to the appearance of symptoms on a particular leaf layer, though less heavy rain may suffice to splash inoculum onto upper leaves in shorter, immature canopies where stem elongation is incomplete. At the fifth site, infection occurred later in May and disease failed to develop to a significant degree. At all sites, the length of the incubation period on any of the top three leaves was found to be between 396 and 496 degree days.
Control of winter epidemics of S. tritici had little effect on yield, whereas spray sequences commencing later than growth stage (GS) 31 but immediately prior to the critical periods provided the best disease control and yield benefit. Regression models incorporating, as independent variables, area under the S. tritici disease progress curve for any of the top three leaves from their emergence (GS 32-37) satisfactorily explained yield loss at the four sites where disease was severe. Consideration of leaf 2 or leaf 3 alone accounted for more than 82% of the variance at each site and a yield loss from infection of leaf 2 related to thermal time is suggested as 0.00265% per C per day from the appearance of symptoms.     

Influence of site factors on yield response of winter wheat to fungicide programmes in England and Wales, 1979–1987

Results of 460 field experiments between 1979 and 1987 incorporating one, two and three fungicide sprays, with a range of active ingredients, were analysed according to site factors including previous crop, sowing date and geographical area. The average untreated yield was 7–48 t/ha, although this fluctuated widely from 6 15 t/ha in 1985 to 9 411 ha in 1984. A single spray at flag-leaf emergence gave an average yield increment of 0 59 t/ha over plots receiving no fungicide. The addition of a second spray at the first-node growth stage gave an extra benefit of 0.22 t/ha, while an additional third spray at ear emergence gave a further 0.28t/ha. The effects on yield of different spray timings were modified by other factors, of which sowing date and previous crop were most important to the first-node spray, and cultivar and geographical area to the ear emergence spray. The data suggest that all crops would benefit economically from a broad-spectrum fungicide applied at flag-leaf emergence. Additionally, crops sown in September, those following winter wheat and those in regions bordering the North Sea respond well at the first-node stage to a fungicide active against eyespot.     

Normal germling development by Erysiphe graminis on cereal leaves freed of epicuticular wax

Experiments were conducted to test the hypothesis that recognition of the physical structure of epicuticular leaf waxes by Erysiphe graminis may be important to the development of normal germlings and the formation of functional appressoria. Comparisons of germination rates and characteristics of germling development by E. graminis f.sp. avenae , and in one experiment by f.sp. hordei , were made between intact cereal leaves and leaves from which the epicuticular waxes had been stripped away.
Overall, fungal development was very similar on intact and wax-free leaves: although germination rates were slightly, but significantly, lower, and lengths of appressorial germ tubes slightly greater, on stripped than intact leaves, a very similar proportion of germlings formed apparently normal appressoria in both cases. This was true for f.sp. avenae on first- and fifth-formed leaves of susceptible and adult plant resistant oats, and on barley and wheat first leaves, and for f.sp. hordei on first leaves of barley, oat and wheat. The appressoria formed on stripped leaves not only appeared normal, but also formed haustoria with at least the same frequency as on intact leaves; in several experiments, a higher proportion formed haustoria in stripped than intact leaves. Wax removal did not affect the adult plant resistance of oat cv. Maldwyn, which limits haustorium formation by appressoria, indicating that epicuticular wax was not involved in this resistance. It is concluded that the physical structure of epicuticular wax is not involved in the recognition processes leading to normal germling development.     

Impact of post-emergence herbicides on weed community diversity within conservation-tillage systems

The influence of herbicides on weed community dynamics is an issue of agroecological concern. A field study was initiated in 1986 with zero-, minimum-, and conventional-tillage systems. In 1989 and 1990, the fourth and fifth years of study, weed community diversity and relative composition were assessed prior to and following the application of post-emergence non-residual herbicides. Weed communities were assessed at the level of tillage system to balance the effect of different crop sequences and crop-herbicide combinations within each comparison. In general, herbicides did not reduce community diversity when compared by Shannon's H’and dominance-diversity curves. An increase in species richness and evenness, as assessed by Shannon's E and Margalef's D_MG occurred in some cases. Differences in relative community composition among tillage systems were apparent before the application of herbicides, but disappeared following herbicide application. The use of herbicides in this study reduced weed densities, maintained weed diversity, and inhibited community changes that were due to changing tillage systems.     

Evaluation of Internal Obturator Muscle Transposition in Treatment of Perineal Hernia in Dogs

A technique that utilizes transposition of the internal obturator muscle for repair of perineal hernias was evaluated. Forty-two male dogs were followed for at least one year after surgery. The repair failed in only one animal, a dog with previously operated bilateral hernias. Microangiography demonstrated an adequate blood supply to the transposed internal obturator muscles of two dogs examined at three weeks and three months after surgery.     

MAGNETIC RESONANCE IMAGING AND PATHOLOGIC FINDINGS ASSOCIATED WITH NECROTIZING ENCEPHALITIS IN TWO YORKSHIRE TERRIERS

Two young adult Yorkshire terriers had neurologic signs consistent with forebrain and brainstem involvement or forebrain involvement alone. On magnetic resonance imaging studies there were asymmetric bilateral lesions mainly in the cerebral cortex, and in the diencephalon. These areas were hyperintense on T2-weighted and FLAIR images, but hypointense or isointense on T1-weighted images. Lesions had a varying degree of contrast enhancement. Areas which were isointense on T1-weighted images had no contrast enhancement or only foci of contrast enhancement. Lesions with hypointensity in T1-weighted images had no enhancement or more frequently ring-like enhancement around the lesion. Necrotizing encephalitis was confirmed pathohistologically in both dogs. The degree of contrast enhancement appeared to be related to the degree of lymphohistiocytic inflammation on histologic examination.     

RADIOBIOLOGICAL AND TREATMENT PLANNING STUDY OF A SIMULTANEOUSLY INTEGRATED BOOST FOR CANINE NASAL TUMORS USING HELICAL TOMOTHERAPY

Feasibility of delivering a simultaneously integrated boost to canine nasal tumors using helical tomotherapy to improve tumor control probability (TCP) via an increase in total biological equivalent uniform dose (EUD) was evaluated. Eight dogs with varying size nasal tumors (5.8-110.9 cc) were replanned to 42 Gy to the nasal cavity and integrated dose boosts to gross disease of 45.2, 48.3, and 51.3 Gy in 10 fractions. EUD values were calculated for tumors and mean normalized total doses (NTD(mean)) for organs at risk (OAR). Normal Tissue Complication Probability (NTCP) values were obtained for OARs, and estimated TCP values were computed using a logistic dose-response model and based on deliverable EUD boost doses. Significant increases in estimated TCP to 54%, 74%, and 86% can be achieved with 10%, 23%, and 37% mean relative EUD boosts to the gross disease, respectively. NTCP values for blindness of either eye and for brain necrosis were < 0.01% for all boosts. Values for cataract development were 31%, 42%, and 46% for studied boost schemas, respectively. Average NTD(mean) to eyes and brain for mean EUD boosts were 10.2, 11.3, and 12.1 Gy3, and 7.5, 7.2, and 7.9 Gy2, respectively. Using helical tomotherapy, simultaneously integrated dose boosts can be delivered to increase the estimated TCP at 1-year without significantly increasing the NTD(mean) to eyes and brain. Delivery of these treatments in a prospective trial may allow quantification of a dose-response relationship in canine nasal tumors.     

Acute onset of pulmonary necrotising arteritis in a dog with a left-to-right patent ductus arteriosus

A 12-week-old, clinically normal Chihuahua was referred for investigation for a continuous heart murmur. Cardiac evaluation revealed an anatomically and haemodynamically typical left-to-right shunting patent ductus arteriosus. The continuous wave Doppler measurement of peak ductal jet velocity of 5.6 m/s was suggestive of a normal pulmonary to systemic arterial pressure ratio. The dog returned 16 days later with right heart failure and severe pulmonary hypertension. Marked reduction in left-to-right shunting was demonstrated and the ductal jet velocity had decreased to 2.5 m/s. Immediate ductus ligation, oxygen therapy before and after the operation, and administration of hydralazine failed to reduce pulmonary hypertension, and the dog was euthanased. Histopathological examination of the lung showed pulmonary necrotising arteritis with acute and chronic arterial lesions. Chronic pulmonary vascular changes related to high flow have been associated with altered nitric oxide and endothelin responses. These changes may be responsible for the acute onset of pulmonary hypertension due to relatively minor vascular insults in some human and veterinary patients with left-to-right shunts. The potential for acute progression supports the recommendations for early ductus ligation and the prognostic importance of detecting pulmonary hypertension presurgically in patent ductus arteriosus patients.