Assessment of genetic diversity and relationships among osmanthus fragrans cultivars using AFLP markers

This study was conducted to reveal genetic diversity among 100 Osmanthus fragrans cultivars using amplified fragment length polymorphism (AFLP) markers. Eight AFLP primer combinations produced a total of 443 polymorphic fragments with an average of 64 per primer combination. The percentage of polymorphic bands (86.81 percent), the resolving power (Rp) (32.71) and the PIC values (0.331) showed the efficiency of used primer combinations. The revealed AFLP makers were effective in distinguishing all the cultivars considered. Cluster analysis were performed to assess patterns of diversity among cultivars and showed the abundant genetic diversity. The overall distribution pattern of molecular variation suggested that 93.33 percent of the total genetic variance was within the identified groups and 6.67 percent of the genetic variation was among the identified groups. Our results showed that AFLP markers are useful for Osmanthus fragrans germplasm discrimination as well as for investigation of genetic diversity and variation. The information will facilitate germplasm identification, conservation and new cultivar development.

Heterose e distâncias genéticas moleculares para a produção de grãos em soja / Heterosis and molecular genetic distances for grain yield in soybeans

Em soja, tem sido relatada a ocorrência de heterose para a produção de grãos, e embora a utilização de cultivares híbridas não seja ainda uma realidade nesta espécie, o conhecimento da heterose é importante para uma pré-seleção de cruzamentos, visto que cruzamentos mais heteróticos estão associados a uma maior divergência entre os genitores. Entretanto, a obtenção de sementes F1 em quantidade suficiente para a avaliação experimental em parcelas é muito difícil e, assim, outros indicadores da ocorrência da heterose poderiam ser muito úteis. Objetivou-se, neste trabalho a avaliação da heterose para a produção de grãos em soja e as suas relações com as distâncias genéticas (DG), obtidas com o marcador molecular AFLP. Seis híbridos F1 oriundos de cruzamentos com diferentes distâncias genéticas (DG) e os respectivos genitores foram avaliados em experimentos com quatro repetições, empregando o delineamento em blocos ao acaso. Foi observada uma grande variação entre os cruzamentos quanto às heteroses, isso é, de 6,29 a 56,50 por cento em relação à média dos genitores ( h mg) e de -0,34 a 51,30 por cento em relação ao genitor superior (h gs). As correlações entre as distâncias genéticas (DG) e as heteroses foram elevadas (r = 0,83 e 0,60, respectivamente, para h mg e h gs), indicando que as distâncias genéticas podem ser utilizadas como indicativas de cruzamentos mais divergentes e, consequentemente, como um dos auxiliares na seleção de genitores mais divergentes em soja.

Heterosis has been reported for grain yield in soybeans, and despite the fact that hybrid cultivars have not been used yet, the knowledge of heterosis magnitude is very important for a previous selection of crosses, since heterosis is related to parental divergence. However, the obtention of enough F1 seeds for experimental evaluation in plots is a time-consuming task, and thus, other indicators of the occurrence of heterosis could be very useful. The objective of this work was to evaluate heterosis and its relationship with AFLP molecular genetic distance (DG). Six F1 hybrids, derived from parents with different levels of genetic distances (DG) and their respective parents, were evaluated in completely randomized block designs, with four replications. Heterosis estimates were very different among different crosses, varying from 6.29 to 56.50 percent for mid-parent heterosis (h mg) and from -0.34 to 51.30 percent for high-parent heterosis (h gs). Besides, the correlation between heterosis and genetic distances (DG) were very high (0.83 and 0.60,respectively, for h mg and h gs), which indicates that DG can be used as indicative of more divergent crosses, and thus, as one criterion for selection of more divergent parents.

An AFLP marker linked to the Pm-1 gene that confers resistance to Podosphaera xanthii race 1 in Cucumis melo

Brazil produced 330,000 metric tons of melons in 2005, principally in the Northeast region where one of the most important melon pathogens is the powdery mildew fungus Podosphaera xanthii. The disease is controlled mainly by incorporating single dominant resistance genes into commercial hybrids. We report on linkage analysis of the Pm-1 resistance gene, introgressed from the AF125Pm-1 Cantalupensis Charentais-type breeding line into the yellow-fleshed melon (Group Inodorus) breeding line AF426-S by backcrossing to produce the resistant line AF426-R, and the amplified fragment length polymorphism (AFLP) marker M75/H35_155 reported to be polymorphic between AF426-S and AF426-R. Segregation analysis of M75/H35_155 using a backcross population of 143 plants derived from [AF426-R x AF426-S] x AF426-S and screened for resistance to P. xanthii race 1 produced a recombination frequency of 4.9 percent, indicating close linkage between M75/H35_155 and Pm-1. Using the same segregating population, the M75/H35_155 marker had previously been reported to be distantly linked to Prv¹, a gene conferring resistance to papaya ringspot virus-type W. Since M75/H35_155 is linked to Prv¹ at a distance of 40.9 cM it is possible that Pm-1 and Prv¹ are also linked.