Global status of wheat leaf rust caused by <Emphasis Type="Italic">Puccinia triticina</Emphasis>

Leaf rust caused by Puccinia triticina is the most common and widely distributed of the three wheat rusts. Losses from leaf rust are usually less damaging than those from stem rust and stripe rust, but leaf rust causes greater annual losses due to its more frequent and widespread occurrence. Yield losses from leaf rust are mostly due to reductions in kernel weight. Many laboratories worldwide conduct leaf rust surveys and virulence analyses. Most currently important races (pathotypes) have either evolved through mutations in existing populations or migrated from other, often unknown, areas. Several leaf rust resistance genes are cataloged, and high levels of slow rusting adult plant resistance are available in high yielding CIMMYT wheats. This paper summarizes the importance of leaf rust in the main wheat production areas as reflected by yield losses, the complexity of virulence variation in pathogen populations, the role cultivars with race-specific resistance play in pathogen evolution, and the control measures currently practiced in various regions of the world.     

Bacterial rhodopsin: evidence for a new type of phototrophy in the sea

Extremely halophilic archaea contain retinal-binding integral membrane proteins called bacteriorhodopsins that function as light-driven proton pumps. So far, bacteriorhodopsins capable of generating a chemiosmotic membrane potential in response to light have been demonstrated only in halophilic archaea. We describe here a type of rhodopsin derived from bacteria that was discovered through genomic analyses of naturally occuring marine bacterioplankton. The bacterial rhodopsin was encoded in the genome of an uncultivated gamma-proteobacterium and shared highest amino acid sequence similarity with archaeal rhodopsins. The protein was functionally expressed in Escherichia coli and bound retinal to form an active, light-driven proton pump. The new rhodopsin exhibited a photochemical reaction cycle with intermediates and kinetics characteristic of archaeal proton-pumping rhodopsins. Our results demonstrate that archaeal-like rhodopsins are broadly distributed among different taxa, including members of the domain Bacteria. Our data also indicate that a previously unsuspected mode of bacterially mediated light-driven energy generation may commonly occur in oceanic surface waters worldwide.     

Use of electrospray mass spectrometry for mass determination of grape (Vitis vinifera) juice pathogenesis-related proteins: a potential tool for varietal differentiation

Methods based on liquid chromatography-mass spectrometry (LC-MS) and protein trap mass spectrometry (trap-MS) were developed to determine the complement of pathogenesis-related (PR) proteins in grape juice. Trap-MS was superior to LC-MS in terms of simplicity, rapidity, and sensitivity. Proteins with a wide range of masses (13--33 kDa) were found in the juices of 19 different varieties of grape (Vitis vinifera) and were identified as mostly PR-5 type (thaumatin-like) and PR-3 type (chitinases) proteins. Although the PR proteins in juices of grapes are highly conserved, small consistent differences in molecular masses were noted when otherwise identical proteins were compared from different varieties. These differences persisted through different harvest years and in fruits grown in different Australian locations. With the definition of four different masses for PR-5 proteins (range = 21,239--21,272 Da) and nine different masses of PR-3 proteins (range = 25,330--25,631 Da) and using statistical analysis, the methods developed could be used for varietal differentiation of grapes grown in several South Australian locations on the basis of the PR protein composition of the juice. It remains to be seen whether this technology can be extended to grapes grown worldwide and to wine and other fruit-derived products to assist with label integrity to the benefit of consumers.     

Differentiation of species from the Penicillium roqueforti group by volatile metabolite profiling

Species from the Penicillium roqueforti group were differentiated by volatile metabolite profiling primarily of sesquiterpenes. A total of 24 isolates from species P. roqueforti, Penicillium carneum, and the recently described species Penicillium paneum were inoculated on yeast extract sucrose agar. Volatile metabolites were collected by diffusive sampling onto tubes containing Tenax TA, overnight between the fifth and sixth days of incubation. Volatiles were thermally desorbed and analyzed by gas chromatography coupled to mass spectrometry. The sesquiterpene area of the chromatogram was investigated, and potential sesquiterpenes were tabulated by comparison of their Kovats retention index and mass spectrum. In general, P. carneum isolates produced the lowest number of sesquiterpenes, all of which were unique for P. carneum within the P. roqueforti group. P. roqueforti and P. paneum produced a larger variety of volatile metabolites, some of which they have in common and some of which are unique for the two species. (+)-Aristolochene was found in samples from P. paneum and P. roqueforti. Other Penicillium species in which (+)-aristolochene was also detected were P. commune, P. glandicola, and P. solitum.     

Studying crossover genotype × environment interaction using linear-bilinear models and mixed models

In agriculture and plant breeding the most important genotype × environment interaction pattern is crossover genotype × environment interaction. Procedures using linearbilinear models are used to find disjoint subsets of sites or genotypes with negligible crossover genotype × environment interaction. In terms of correlations, these subsets of sites or genotypes should be such that pairs of sites have nearly perfect positive genetic correlations. Perfect positive genetic correlation between sites is a sufficient, but not a necessary, condition for a non-COI pattern. The main objective of this study was to use the mixed model theory to confirm that the subsets of sites and genotypes formed by using the linear-bilinear models have negligible crossover genotype × environment interaction. If there is no significant crossover interaction in a subset of sites or genotypes, then the mixed model should be able to confirm this by nonrejection of the hypothesis that the covariance structure has perfect genetic correlation. Mixed model analysis of results from two multisite cultivar trials confirmed the validity of the procedures using linear-bilinear model methods for clustering sites and genotypes into noncrossover genotype × environment interaction subsets.     

N-acetyl-beta-D-glucosaminidase and antitrypsin in subclinically infected quarter-milk samples: effect of bacteria and hemolysins, lactation stage, and lactation number

Interrelationships between N-acetyl-beta-D-glucosaminidase (indicating cellular damage) and antitrypsin (indicating increased permeability between the blood and milk compartments) were evaluated in 1,411 quarter-milk samples collected during routine herd surveys. N-Acetyl-beta-D-glucosaminidase was antitrypsin, whereas, in more severe mastitis, antitrypsin had a more constant deflection. The sensitivity of both determinants was associated with the virulence of bacteria. Production of bacterial hemolytic toxins was associated with a significant increase in both determinants. Penicillinase production by staphylococci was associated with selective increases of antitrypsin.     

Bacterial growth in whey from mastitic and nonmastitic quarters

Growth of Escherichia coli and Staphylococcus aureus was analyzed by turbidometry in 456 selected whey samples. The samples had been graded mastitic or nonmastitic as determined by antitrypsin assay and bacteriologic examination. Whey samples from inflamed quarters (antitrypsin increased) and infected quarters significantly promoted bacterial growth as compared with whey samples from control quarters. The growth-stimulatory effect was limited to the diseased quarters, since control quarters from the same animals did not support enhanced bacterial growth. The observations indicate that in chronic mastitis, the inflammatory process leads to changes in the whey that promote bacterial growth in vitro.     

A Cross-sectional Study of Reproductive Performance of Smallholder Dairy Cows in Coastal Tanzania

A retrospective cross-sectional study was conducted on 200 randomly selected smallholder farms from a mixed dairy farming system in Tanga, Tanzania, between January and April 1999. We estimated the frequency and determinants of long calving interval (LCI), retention of fetal membrane (RFM), dystocia, and abortion in smallholder crossbred cattle and explored birth trends. The mean calving interval was 500 days and birth rate was 65 per 100 cow-years. Dystocia was reported to affect 58% of calvings, and 17.2% of animals suffered RFM. Using mixed effect models, the variables associated with LCI, RFM and dystocia were breed, level of exotic blood and condition score. Zebu breeding was associated with LCI (odds ratio (OR) = 2.3, p = 0.041) and Friesian breeding with lower odds for RF (OR = 0.26, p = 0.020). Animals with higher levels of exotic blood had lower odds for evidence of dystocia (OR = 0.45, p =0.021). Evidence of dystocia was significantly associated with poor condition score (P = −1.10, p = 0.001). Our observations suggest that LCIs are common in smallholder dairy farms in this region and a likely source of economic loss. Dystocia, RFM, poor condition score and mineral deficiency were common problems and were possibly linked to LCI.