Adaptive molecular evolution of a defence gene in sexual but not functionally asexual evening primroses.

Theory predicts that sexual reproduction provides evolutionary advantages over asexual reproduction by reducing mutational load and increasing adaptive potential. Here, we test the latter prediction in the context of plant defences against pathogens because pathogens frequently reduce plant fitness and drive the evolution of plant defences. Specifically, we ask whether sexual evening primrose plant lineages (Onagraceae) have faster rates of adaptive molecular evolution and altered gene expression of a class I chitinase, a gene implicated in defence against pathogens, than functionally asexual evening primrose lineages. We found that the ratio of amino acid to silent substitutions (K(a) /K(s) = 0.19 vs. 0.11 for sexual and asexual lineages, respectively), the number of sites identified to be under positive selection (four vs. zero for sexual and asexual lineages, respectively) and the expression of chitinase were all higher in sexual than in asexual lineages. Our results are congruent with the conclusion that a loss of sexual recombination and segregation in the Onagraceae negatively affects adaptive structural and potentially regulatory evolution of a plant defence protein.

Cryphonectriaceae (Diaporthales), a new family including Cryphonectria, Chrysoporthe, Endothia and allied genera.

Recent phylogenetic studies on the members of the Diaporthales have shown that the order includes a number of distinct phylogenetic groups. These groups represent the Gnomoniaceae, Melanconidaceae, Valsaceae, Diaporthaceae and Togniniaceae. New groups representing undescribed families also have emerged and they have been referred to as the Schizoparme, Cryphonectria-Endothia and Harknessia complexes. In this study we define the new family Cryphonectriaceae (Diaporthales) to accommodate genera in the Cryphonectria-Endothia complex. These genera can be distinguished from those in other families or undescribed groups of the Diaporthales by the formation of orange stromatic tissue at some stage of their life cycle and a purple reaction in KOH and a yellow reaction in lactic acid associated with pigments in the stromatic tissue or in culture.

Biological and Phylogenetic Analyses Suggest that Two Cryphonectria spp. Cause Cankers of Eucalyptus in Africa.

Cryphonectria cubensis is an economically important pathogen of commercial Eucalyptus spp. Differences have been reported for disease symptoms associated with Cryphonectria canker in South Africa and other parts of the world, and recent DNA-based comparisons have confirmed that the fungus in South Africa is different from that in South America and Australasia. During a disease survey in the Republic of Congo, Cryphonectria canker was identified as an important disease on Eucalyptus grandis and E. urophylla. In this study, we compared Congolese and South African isolates of C. cubensis using DNA sequence data and pathogenicity under greenhouse conditions. The ß-tubulin and internal transcribed spacer (ITS) region sequences show that C. cubensis in Congo is different from the fungus in South Africa and that Congolese isolates group most closely with South American isolates. Furthermore, pathogenicity tests showed that a South African isolate was more aggressive than two Congolese isolates. We conclude that two distinct Cryphonectria spp. occur in Africa and hypothesize that the fungus in the Congo probably was introduced into Africa from South America. Both fungi are important pathogens causing disease and death of economically important plantation trees. However, they apparently have different origins and must be treated separately in terms of disease management and quarantine considerations.