HERITABILITY OF CLOVER ROT RESISTANCE (SCLEROTINIA SPP.) IN RED CLOVER (TRIFOLIUM PRATENSE) POPULATIONS.

European red clover (Trifolium pratense) crops are susceptible to clover rot, a destructive disease caused by Sclerotinia trifoliorum or S. sclerotiorum. The lack of knowledge on the heritability of clover rot resistance is, among other reasons, responsible for the slow progress of resistance breeding. In this paper, we acquired insight in the heritability of clover rot resistance through divergent selection by our high-throughput bio-test on an experimental diploid population. The disease susceptibility indices of the first generation after selection for susceptibility and the first and the second generation after selection for resistance were compared with the susceptibility of the original population. The susceptible population (79.2%), the original population (70.5%) and the first generation resistant population (62.3%) differed significantly in susceptibility (p < 0.001). The first (62.3%) and second generation resistant population (60.0%) did not differ significantly in susceptibility. The heritability (h2) of clover rot resistance was low: 0.34 and 0.07 in the first and second cycle of selection respectively. This indicates that mass selection is not suitable to improve clover rot resistance. Family selection may allow a sustained increase in resistance for multiple generations.

Evaluation of a diverse red clover collection for clover rot resistance (Sclerotinia trifoliorum).

Sclerotinia trifoliorum Erikks. causes clover rot (clover cancer, Sclerotinia crown and root rot), an important disease in European red clover crops (Trifolium pratense L). The fungus infects plants in autumn through ascospores and entire fields can be destroyed by early spring. Although previous studies have evaluated various red clover populations for clover rot resistance, screening was often performed with one local isolate on just a few local varieties, often cultivars. Until today, no large collections of diverse red clover accessions have been screened. In this study, we studied the variation in clover rot susceptibility among 122 red clover accessions, including 85 accessions from the NPGS-USDA core collection. Cultivars (both diploid and tetraploid), landraces and wild accessions were included and different S. trifoliorum isolates were used. In a field experiment, plant yield, branching and susceptibility to mildew, rust and virus disease were scored for 122 red clover accessions. A similar collection of germplasm was screened for clover rot resistance by a bio-test on young plants using a mixture of five aggressive S. trifoliorum isolates. The effects of the variety type, ploidy level, growth habit, resistance to other diseases and levels of isoflavones (available for the NPGS-USDA collection) on clover rot susceptibility were determined. Possible sources of resistance were identified. Our red clover accessions differed significantly in susceptibility but no accession was completely resistant Three accessions (Maro, Tedi and No. 292) were significantly less susceptible than the other accessions. Intensive branching or a prostrate growth habit did not render plants more resistant. Accessions resistant to mildew or viruses were not more resistant to clover rot and accessions with high levels of isoflavones were not better protected against clover rot. On the other hand, tetraploid cultivars were on average 10% less susceptible than diploid cultivars. Cultivars were generally less susceptible than landraces and wild accessions. Allocating sources of resistance for breeding purposes is difficult. The best way to improve clover rot resistance may be to select and intercross resistant plants from cultivars with low susceptibility.

Aggressiveness study on Sclerotinia isolates from red clover crops.

Sclerotinia trifoliorum Erikks. causes clover rot (clover cancer, Sclerotinia crown and root rot) in red clover crops (Trifolium pratense L.), an important disease in Europe. Little is known about the aggressiveness of Scierotinia isolates and aggressiveness studies were never conducted on a European scale. In this study we compared the aggressiveness of 30 Sclerotinia isolates isolated from red clover crops in 25 locations in 12 European countries using a plant-based bio-test. Plants from 6 red clover cultivars with different resistance levels were spray inoculated at the age of 12 weeks with 1 to 1.5 ml mycelium fragment suspension per plant. After 10 days incubation, plants were scored on a scale from 1 (healthy plant) to 5 (dead plant) and the disease index was calculated. The experiment was repeated 3 times and all repetitions were highly correlated. Average disease indices ranged from 52.6% to 82.7%. Significant differences were detected between isolates and between cultivars, but there was no isolate--cultivar interaction. Based on these results, the most aggressive isolates can be selected for resistance breeding. Future work should investigate whether the differences in aggressiveness are due to a higher growth speed or due to a higher secretion of cell-wall degrading components and pathogenicity factors.

Construction of a bio-test for infecting red clover plants with Sclerotinia trifoliorum.

Sclerotinia trifoliorum causes clover cancer in red clover crops. Clover cancer is difficult to control and completely resistant red clover varieties are not available. Breeding for resistant red clover varieties is being slowed down because little is known about the diversity of European S. trifoliorum populations and because of the lack of bio-tests that are useable in breeding programs. The first objective of this research was to develop a reliable high-throughput bio-test, useable in breeding programs. The second objective was to optimise another bio-test, based on isolated leaves, for more precise studies. First, we optimised a method for ascospore production of S. trifoliorum. Once produced, the ascospores were used to evaluate the effects of climate conditions, ascospore concentration and plant age on the high-throughput bio-test. For the bio-test on isolated leaves, the effects of infection method, incubation conditions, incubation period, ascospore concentration, leaf growth stage and mechanical damage were evaluated. In the high-throughput bio-test, disease levels rose with increasing ascospore concentration up to 20,000 spores/ml. The plant age had a small, yet significant effect on the disease level. For the isolated leaf bio-test, the most effective and most repeatable infection method was spraying of an ascospore suspension. Disease levels continued to increase with rising concentrations and incubation time did not interact with plant susceptibility levels. The youngest completely opened leaf yielded the most repeatable results. Both bio-tests were shown to be correlated and could be valuable instruments for breeding programs and for studying plant-pathogen interactions.

Diversity study on Sclerotinia trifoliorum Erikks., the causal agent of clover rot in red clover crops (Trifolium pratense L.).

Since the 16th century, red clover has been an important crop in Europe. Since the 1940s, the European areal of red clover has been severely reduced, due to the availability of chemical fertilizers and the growing interest in maize. Nowadays there is a growing interest in red clover again, although some setbacks still remain. An important setback is the low persistence of red clover crops. Clover rot, caused by the ascomycete fungus Sclerotinia trifoliorum Erikss., is a major disease in Europe and reduces the persistence of red clover crops severely. The fungus infects clover plants through ascospores in the autumn, the disease develops during the winter and early spring and can kill many plants in this period. In early spring, black sclerotia, serving as surviving bodies, are formed on infected plants. Sclerotia can survive up to 7 years in the soil (Ohberg, 2006). The development of clover rot is highly dependent on the weather conditions: a humid fall, necessary for the germination of the ascospores and an overall warm winter with short periods of frost are favourable for the disease. Cold and dry winters slow the mycelial growth down too much and prevent the disease from spreading. Clover rot is difficult to control and completely resistant red clover varieties have yet to be developed. Because of the great annual variation in disease severity, plant breeders cannot use natural infection as an effective means to screen for resistant material. Breeding for resistant cultivars is being slowed down by the lack of a bio-test usable in breeding programs. When applying artificial infections, it is necessary to have an idea of the diversity of the pathogen. A diverse population will require resistance screening with multiple isolates. The objective of this research is to investigate the genetic diversity among isolates from the pathogen S. trifoliorum from various European countries. We assessed diversity using a species identification test based on the sequence of the beta-tubulin gene, vegetative compatibility grouping and AFLP.

Stereoscopic vision provides a significant advantage for precision robotic laparoscopy.

BACKGROUND: Current surgical robots provide no sense of touch and rely solely upon vision. This study evaluated the effect of new stereoscopic technology on the performance of robotic precision laparoscopy. METHODS: Eight experienced laparoscopists with no experience in robotics performed five tasks of increasing complexity using a laparoscopic robot. The tasks were as follows: rope pass, paper cut, needle capping, knot tying and needle threading. Each test was performed ten times under both stereoscopic and monoscopic conditions. Performance times and errors were recorded. RESULTS: Mean(s.e.m.) final performance times were calculated from the final five trial times for each test, and were as follows for monoscopic and stereoscopic conditions respectively: rope pass 112.8(4.2) and 97.0(3.7) s (P = 0.013), paper cut 117.1(6.0) and 98.4(9.8) s (P = 0.020), needle capping 144.5(12.7) and 99.7(6.8) s (P = 0.008), knot tying 138.7(14.3) and 70.3(6.0) s (P = 0.002), and needle threading 210.8(28.2) and 92.3(4.1) s (P = 0.002). The mean(s.e.m.) number of errors per candidate was 60.6(7.8) and 20.8(3.9) under monoscopic and stereoscopic conditions respectively (P = 0.004). CONCLUSION: Stereoscopic vision provided a significant advantage during robotic laparoscopy in situations that required a precise understanding of structural orientation.