First insight into genetic diversity and population structure of the Caucasian wild apple (<Emphasis Type="Italic">Malus orientalis</Emphasis> Uglitzk.) in the Hyrcanian forest (Iran) and its resistance to apple scab and powdery mildew

Investigating population genetic structure and diversity, and resistance to pathogens in crop wild relatives are key steps to assess appropriate conservation and breeding programs. The Caucasian wild apple (Malus orientalis Uglitzk.) is an emblematic fruit tree of the Hyrcanian forest and is supposed to be a contributor to the cultivated apple genome (Malus domestica Borkh. Yet, no study has investigated its population structure, diversity and susceptibility to the two main pathogens of apples, the apple scab (Venturia inaqualis) and the powdery mildew (Podosphaera leucotricha). Here, we investigated population genetic structure and diversity of M. orientalis in the Hyrcanian forest as a mean to identifying future targeted populations for apple conservation and breeding programs. We genotyped using multilocus microsatellite 100 M. orientalis trees sampled in 14 sites. These trees were also screened for presence/absence of six (Rvi6, Vr, Rvi4, Rvi15, Rvi5 and Rvi11) and three (Pl-1, Pl-w, Pl-d) resistance genes to the apple scab and the powdery mildew respectively. Our results showed significant but weak between-site genetic differentiation and isolation by distance pattern suggesting substantial historical gene flow for M. orientalis in this area. We also detected a West-Eastern genetic structure across the Hyrcanian forest with five main populations showing admixture. We also showed a high diversity of resistance genes to apple scab across sites; in contrast, we only found one resistance gene to powdery mildew. These results are a first glimpse to settle wild apple conservation programs in Iran and pinpoint Iranian wild apple populations as an untapped source for apple breeding.     

Local maladaptation of the anther-smut fungus parasitizing Dianthus carthusianorum

Pathogens are generally expected to evolve faster than their hosts and are therefore likely to be locally adapted. However, some pathogens might lag behind in the co-evolutionary arms race because they do not have some of the advantages shared by most other pathogens (e.g., high mutation or recombination rates, short generation time, high dispersal ability). This is the case of Microbotryum fungi that cause the anther smut disease in plants of the family Caryophyllaceae. We investigated the patterns of local adaptation and maladaptation in Microbotryum carthusianorum and its host plant Dianthus carthusianorum. We performed a full cross-inoculation experiment using half-sib plant families and fungal samples originating from three naturally infected populations in the Czech Republic. We specifically asked, which components of pathogen fitness (i.e., infectivity and host manipulation) are affected by local (mal)adaptation. The pathogen was on average 1.6 times more successful in infecting plants from foreign populations compared to plants from its home population. Once the infection was successful, the pathogen accelerated the plant’s flowering and thus increased the opportunity for transmission to new hosts. However, the level of manipulation of host flowering did not differ between home and foreign populations. This study showed that the pathogen’s infectivity followed a clear pattern of local maladaptation, whereas the host manipulation did not. Our study taken together with previous studies of a related anther smut species reveals the pervasiveness of local maladaptation in this group of pathogens that arises as the result of their restricted gene flow and reduced recombination rates.