Fitness Cost and Competitive Ability to Different Ploidy Levels in Ryegrass Genotypes

ABSTRACT: The intergenotypic competition of tetraploid ryegrass with natural diploid population may be a tool to reduce the frequency of resistant individuals in an area. This study aimed to identify and compare the phenological development, fitness cost, and competitive ability between diploid and tetraploid ryegrass genotypes. Genotypes were grown in pots, and the morphological variables of genotype growth were assessed every 15 days up to 120 days after emergence to evaluate the fitness cost. Phenological development and seed yield components were measured in a single time together with the fitness cost. Competitive ability was determined in a replacement-series experiment with proportions of tetraploid and diploid ryegrass, in which the number of tillers, plant height, leaf area, and shoot dry weight were assessed at 50 days after emergence. The results of fitness cost showed that the number of tillers, leaf area, root dry weight, and the number of seeds were higher for tetraploid ryegrass, which presented a higher competitive ability than the diploid genotype regardless of the tested proportions. Tetraploid ryegrass may be useful for reducing the frequency of herbicide-resistant diploid ryegrass because of its higher competitive potential.

Multiple Human Papilloma Virus Infections and Their Impact on the Development of High-Risk Cervical Lesions

Objective: Individuals are often infected with multiple genotypes of human papillomavirus (HPV) simultaneously, but the role these infections play in the development of cervical disease is not well established. This study aimed to determine the association of multiple HPV infections with high-risk cervical lesions (hrCLs). Study Design: HPV genotyping was performed on 798 SurePath specimens collected between December 1, 2009, and April 30, 2011. The cases were classified as hrCL (n = 90) or non-hrCL (n = 708) based on cytology diagnoses. The association between hrCL and HPV infection patterns was analyzed. Results: Multiple HPV infections were frequently encountered (38.2%) in the cohort. Increased frequency of hrCLs was associated with a single high-risk HPV (hrHPV) infection. An additive or synergistic effect was not observed for hrCL in multiple HPV infections. The hrCL rates appeared to decrease in various patterns of multiple HPV infections, but the reduction was not statistically significant. Conclusions: Multiple HPV infections are common with no additive or synergistic effect on the development of hrCL. Conversely, reduced hrCL rates were observed in various patterns of multiple HPV infections compared to their single-genotype infection counterparts, suggestive of possible intergenotypic competition or more effective immune response triggered by multiple infections. Further studies in larger cohorts are needed.

Early selection in open-pollinated Eucalyptus families based on competition covariates

The objetive of this work was to evaluate the influence of intergenotypic competition in open-pollinated families of Eucalyptus and its effects on early selection efficiency. Two experiments were carried out, in which the timber volume was evaluated at three ages, in a randomized complete block design. Data from the three years of evaluation (experiment 1, at 2, 4, and 7 years; and experiment 2, at 2, 5, and 7 years) were analyzed using mixed models. The following were estimated: variance components, genetic parameters, selection gains, effective number, early selection efficiency, selection gain per unit time, and coincidence of selection with and without the use of competition covariates. Competition effect was nonsignificant for ages under three years, and adjustment using competition covariates was unnecessary. Early selection for families is effective; families that have a late growth spurt are more vulnerable to competition, which markedly impairs ranking at the end of the cycle. Early selection is efficient according to all adopted criteria, and the age of around three years is the most recommended, given the high efficiency and accuracy rate in the indication of trees and families. The addition of competition covariates at the end of the cycle improves early selection efficiency for almost all studied criteria.

Plot size matters: interference from intergenotypic competition in plant phenotyping studies

Genetic and physiological studies often comprise genotypes diverse in vigour, size and flowering time. This can make the phenotyping of complex traits challenging, particularly those associated with canopy development, biomass and yield, as the environment of one genotype can be influenced by a neighbouring genotype. Limited seed and space may encourage field assessment in single, spaced rows or in small, unbordered plots, whereas the convenience of a controlled environment or greenhouse makes pot studies tempting. However, the relevance of such growing conditions to commercial field-grown crops is unclear and often doubtful. Competition for water, light and nutrients necessary for canopy growth will be variable where immediate neighbours are genetically different, particularly under stress conditions, where competition for resources and influence on productivity is greatest. Small hills and rod-rows maximise the potential for intergenotypic competition that is not relevant to a crop’s performance in monocultures. Response to resource availability will typically vary among diverse genotypes to alter genotype ranking and reduce heritability for all growth-related traits, with the possible exception of harvest index. Validation of pot experiments to performance in canopies in the field is essential, whereas the planting of multirow plots and the simple exclusion of plot borders at harvest will increase experimental precision and confidence in genotype performance in target environments.

Combined effects of disease and competition on plant fitness

Wheat genotypes susceptible to different races of a pathogen, Puccinia striiformis, were planted in pure stands and in three different 1:1 mixtures, in both the presence and absence of disease, in two sites, and over 3 years. Using analyses of variance, we tested whether disease and intergenotypic competition influenced a genotype's fitness and whether significant interactions existed between the effects of disease and competition on genotype fitness. Seed weight, number of inflorescences per seed planted, seeds per inflorescence, and absolute fitness were estimated for each genotype in each treatment. Absolute fitness was determined as the number of seeds collected per seed planted. Disease reduced seed weight. The other fitness measures were influenced by either disease or competition, and the impact of each factor often varied among site-year combinations. In general, interactions between the effects of disease and competition on genotype fitness were not significant. The few significant interactions indicated a less than additive effect of competition and disease on genotype fitness. The overall lack of interaction may be, in part, due to lesser disease levels in mixed as compared with pure stands, or reduced level of competition under diseased conditions.Key words: pathogens, competition, plant fitness, stripe rust, wheat.