The Panama Tall and the Maypan hybrid coconut in Jamaica: did genetic contamination cause a loss of resistance to Lethal Yellowing?

We applied Bayesian population assignment methods to assess the trueness to type of four populations of the coconut cultivar Panama Tall (PNT) located in Jamaica and found that two of them presented a high percentage of off-types, while genetic contamination was low in the two others. The PNT is the pollen parent of the MAYPAN hybrid, which used to be planted in Jamaica to control an epidemic disease: Lethal Yellowing. The main source of contamination was the susceptible Jamaica Tall, thus increasing the susceptibility in the resulting MAYPAN progeny. The incidence of genetic contamination seems however to be insufficient to be the only cause of the latest outbreak of the disease. Neither the MAYPAN nor its parents can be said resistant in the present context of Jamaica.     

AFLP data suggest a potential role for the low genetic diversity of acid lime (Citrus aurantifolia Swingle) in Oman in the outbreak of witches’ broom disease of lime

Acid lime (Citrus aurantifolia) is the fourth largest fruit crop in terms of cultivated area and production in Oman. However, over half a million lime trees were lost in Oman over the past 35?years due to witches?? broom disease of lime (WBDL) which is caused by Candidatus phytoplasma aurantifolia. This study was conducted to examine genetic diversity of acid lime in Oman. AFLP analysis of 143 acid lime samples from Oman, 2 from Brazil and one from Pakistan using 4 primer pair combinations produced 980 polymorphic loci (100?%) and 146 AFLP genotypes. Despite the long history of acid lime cultivation in Oman, populations of lime from different districts were found to have low levels of genetic diversity (0.0888?C0.2284). AMOVA analysis indicated the existence of high level of genetic differentiation (F _ST?=?0.271) among populations of acid lime from Oman and Brazil, which indicates that both populations have evolved independently for a considerably long period of time. On the other hand, AMOVA analysis showed that only 11?% of the genetic variation exists among populations from the 18 different districts in Oman. This suggests frequent exchange of acid lime planting material across geographical regions in Oman. Findings from this study suggest that the low level of genetic diversity of acid lime in Oman and frequent movement of acid lime planting material across districts are two main factors which contributed to the rapid spread and high susceptibility of acid limes to WBDL in the country.     

Effect of some environmental factors on the appearance of “June Yellows” in strawberries and its significance for the development of a test method

Summary The symptoms of June Yellows in strawberries only appear in spring and autumn, and vary in extent from year to year. In order to find a test method for June Yellows which would make it possible to produce yellows symptoms independently of the weather conditions, an investigation of the climatic factors favouring the appearance of yellows was started.It proved possible to produce in apparently normal plants of the varieties Auchincruive and Blakemore symptoms of both Transient Yellows and Streak by growing them at 5°C and providing artificial light of about 7000 lux for at least 12 hours per day.For plants from an environment with a relatively low temperature a treatment of about two months proved sufficient to produce a maximum effect. For plants from an environment with a relatively high temperature a treatment of about three months was necessary to obtain a maximum reaction.

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Samenvatting De symptomen van voorjaarsbont bij aardbeien treden uitsluitend op in het voorjaar en najaar, maar in verschillende jaren in verschillende mate. Teneinde de beschikking te krijgen over een toetsmethode op Voorjaarsbont, waarbij onafhankelijk van toevallige weersomstandigheden bontsymptomen kunstmatig geproduceerd kunnen worden, is een onderzoek ingesteld naar klimaatsfactoren welke het optreden van bont begunstigen.Het bleek mogelijk om bij uiterlijk normale planten van de rassen Auchincruive Climax en Blakemore symptomen zowel van Transient Yellows als van Streak te voorschijn te roepen door ze te plaatsen in een omgeving met een temperatuur van 5°C en een belichting van ±7000 lux gedurende minstens 12 uren per etmaal. Voor planten afkomstig uit een koude omgeving bleek een behandeling van ongeveer twee maanden voldoende te zijn om een maximaal effect te bereiken, bij planten uit een warme omgeving was voor een maximale reactie een behandeling van ongeveer drie maanden nodig.

     

Identifying the impact of multi-hazards on crop yield—A case for heat stress and dry stress on winter wheat yield in northern China

Winter wheat production in northern China severely suffered from high temperatures and low relative humidity. However, the spatio-temporal pattern of heat stress and dry stress and the impacts of these multi-hazards on winter wheat yield have rarely been investigated. Using historical climate data, phenology data and yield records from 1980 to 2008, an analysis was performed to characterize the spatio-temporal variability of heat stress and dry stress in the post-heading stages of wheat growth in northern China. Additionally, these stresses’ impacts on winter wheat yield fluctuations were evaluated. Spatially, the central and northern parts of northern China have seen more serious heat stress, while greater dry stress has been observed in the northwest and north of the research area. Temporally, the heat stress has increased in the western part but decreased in the central and eastern parts of research area. Dry stress has aggravated in the entire northern China during the past decades, indicating the complexity of the exposure to adverse climate conditions. These two hazards (heat stress and dry stress) have contributed significant yield loss (up to 1.28% yield yr⁻¹) in most parts of the research region. The yield in the west was more sensitive to heat stress, and dry stress was the main hazard in the south. Additionally, the opposite spatial pattern between the sensitivity and exposure revealed that the climate is not the only factor controlling the yield fluctuation, the local adaptation measures used to mitigate negative influences of extreme events should not be ignored. In general, this study highlighted a focus on the impacts of multi-hazards on agricultural production, and an equal importance of considering local adaptation ability during the evaluation of agricultural risk in the future. Additionally, paying more attention to higher sensitive areas and to more reasonable and practical adaptive strategies is critical and significant for food supply security.     

Assessing the importance of genotype × environment interaction for root traits in rice using a mapping population III: QTL analysis by mixed models

The phenotypic analysis of field experiments includes information about the experimental design, the randomization structure and a number of putative dependencies of environment and design factors on the trait investigated. In QTL studies, the genetic correlation across environments, which arises when the same set of lines is tested in multiple environments, plays an important role. This paper investigates the effect of model choice on the set and magnitude of detected root QTL in rice. Published studies on QTLs for root traits indicate that different results are obtained if varying genetic populations are used and also if different environmental conditions are included. An experiment was conducted with 168 RILs of the Bala × Azucena mapping population plus parents as checks under four environmental conditions (low light, low nitrogen, drought and a control environment). We propose a model that incorporates all relevant experimental information into a composite interval mapping approach based on a mixed model, which especially considers the correlation of genotypes in different environments. An extensive sequential model selection procedure was applied based on the phenotypic model, using the AIC to determine an appropriate random structure and Type 3 Wald F-tests for selection of fixed effects. In a first step we checked whether any of the fixed effects and random (nested) design effects could be dropped. Secondly, an appropriate covariance structure was chosen for genotype × environment interaction. In a third step Box-Cox transformations were applied based on residual analysis. We compared profiles of composite interval mapping scans with and without the inclusion of genotype × environment interaction and the experimental design information. Some distinct differences in profiles indicate that insufficient modeling of the non-QTL part can lead to an overly optimistic interpretation of QTL main effects in interval mapping. It is concluded that mixed model QTL mapping offers a reasonable way to separate environmental and genetic influences in the evaluation of quantitative genes and especially enables a more realistic assessment of QTL and QTL × environment effects than standard approaches by including all relevant effects.