To date, B. cinerea biocontrol products are mostly Bacillus subtilis-based, but their use in commercial strawberry production is limited because of their insufficient applicability in the field or supply chain . Nevertheless, there is social and scientific interest in using biocontrol against B. cinerea as an alternative to chemical pesticides. Isolates of Colletotrichum gloeosporioides, Epicoccum purpurascens, Gliocladum roseum, Penicillium sp., Trichoderma sp. have displayed high efficiency in controlling B. cinerea and were reported to reduce grey mould incidence on strawberry stamens by 79%–93% and on fruit by 48%–76% . Interestingly, in some experiments, the efficiency of biocontrol by these organisms exceeded the efficacy of control via the fungicide captan. Similar results were obtained for other microbes, such as the yeasts A. pullulans and Candida intermedia , the filamentous ascomycete Ulocladium atrum , or the bacterium Bacillus amyloliquefaciens . Biocontrol via microbes can work via different modes of action, including competition for nutrients, secretion of antibiotic compounds and induction of host defence mechanisms like the up-regulation of chitinase and peroxidase activity . Because biocontrol of B. cinerearelies on a variety of mechanisms, the most significant effects are observed when different organisms are applied in combination . As alternative to applying living microbes, use of extracts or volatiles derived from biocontrol microbes has been suggested . Use of non-synthetic antifungal substances, growing blueberries like phenol-rich olive oil mill wastewater, has also been reported to control B. cinerea growth in vitro and on strawberries .
However, these approaches are not implemented on a commercial scale due to high costs compared to the conventional B. cinerea control.It is common practice to handpick strawberries and place them into clamshells in the field, in order to reduce wounding and bruising of the fruit. Rapid and constant cooling of strawberries at temperatures below 2.5 ºC is another critical strategy to reduce or inhibit reactivation of B. cinerea quiescent infections . Often, strawberries are also stored in modified atmospheres, which are generally low in oxygen and high in carbon dioxide to slow down metabolic processes, senescence and fungal decay . Relative humidity during storage is usually kept around 85%–90% to prevent dehydration of fruit, but limit fungal growth . Novel post harvest treatments of strawberries have been suggested to prevent B. cinerea infections during storage. Examples are edible fruit coatings of chitosan, silk fibroin or methylcellulose that prevent water loss and can include antifungal compounds . MeJA treatment to induce fruit defence mechanisms , ultraviolet and visual light treatment , enrichment of storage atmosphere with chlorine or ozone , and soft mechanical stimulation have also been tested as alternative treatments. Most of these approaches are still in an experimental stage or not yet adaptable to commercial settings.Several aspects of the genetics of resistance to B. cinerea are unclear in strawberry. Significant phenotypic variation of incidence or severity of grey mould has been reported; however, F. x ananassa genotypes appear to be universally susceptible and complete resistance has not been observed .
Substantial genotypic variation has not been documented and the heritability of resistance to B. cinerea is unknown. Mild phenotypic differences in fruit resistance levels reported in various post harvest studies indicate that genetic variation for resistance may be limited and that its heritability is low. A contributing factor is the intrinsic characteristics of the pathogen, its broad host range, diverse ways of infection and necrotrophic lifestyle, which explain the absence of a gene-for-gene resistance of strawberry to B. cinerea . Therefore, breeding for escape and tolerance, which includes physiological and biochemical traits, is a more practical option . While limited in scale and scope, earlier studies strongly suggest that the incidence and progression of B. cinerea infections differ between cultivars with soft fruit and those with firm fruit . Hence, previously reported differences amongst cultivars could be the result of the pleiotropic effects of selection for increased fruit firmness and shelf life and the associated developmental and ripening changes, as opposed to direct genetic gains in innate resistance to the pathogen. As discussed, fruit firmness is an important trait associated with resistance to B. cinerea . The strawberry germplasm displays natural variation for fruit firmness and developing cultivars with firmer fruit is an important aim in breeding programmes . Changes in flower morphology could also enhance tolerance to B. cinerea. In strawberry, most B. cinerea infections in fruit appear to originate from primary infections of flowers or secondary infections caused by direct contact with infected flower parts .
It was reported that removal of stamen and petals result in lower grey mould incidence . Faster abscission of flower parts, especially petals, has the potential to aid the escape of strawberries from B. cinerea infections . Similarly, plants with pistillate flowers have a lower grey mould incidence in fruit . B. cinerea growth inhibition in stamens is reported to vary within the strawberry germplasm, potentially due to differences in their biochemical composition . Similarly, antifungal compounds in fruit can prevent or limit B. cinerea infections. Several reports indicate that anthocyanin accumulation contributes to tolerance of strawberries to B. cinerea . Anthocyanins do not just improve tolerance to grey mould but also provide health benefits . Breeding for higher anthocyanin content in strawberries is possible and facilitated by existing variation in the germplasm . Inducing anthocyanin accumulation in flowers could also help to limit flower infections. As breeding for higher B. cinerea tolerance will be tedious and likely will not result in complete resistance, complementary approaches should be considered. Currently, no genetically modified strawberry cultivars are commercially grown; however,several reports show great potential to improve tolerance to grey mould via trans- or cis-genesis. For example, the expression of chitinases or PGIPs from other organisms in strawberries can prevent or slow down fungal infections . Another potential transgenic approach is to increase fruit firmness by altering the expression or activity of pectin degrading enzymes, such as PL or PG . The existing natural variation of PL expression levels and activity in the cultivated strawberry germplasm could be used for cisgenic approaches. Increasing phenolic levels in strawberries by genetic modifications can also be explored as the transcription factor MYB10 was identified as a regulator of anthocyanin levels in strawberries ; Medina-Puche et al., 2014. Transgenic plants with ectopic overexpression of MYB10 show elevated anthocyanin levels throughout the entire plant ; however, the resistance of these plants against B. cinerea have not been tested. In summary, these novel breeding approaches should be supported by integrative management strategies including horticultural and agronomic practices, and potentially biocontrol, to achieve maximum control of the disease.The exceptional levels of biological diversity found on oceanic islands have been the focus of scientific research since the 19th century . The vast majority of oceanic islands are of volcanic origin and were never part of continental landmasses, unlike other types of islands; terrestrial biotas on oceanic islands are therefore generally the result of long-distance dispersal, often followed by in situ speciation, a condition that has stimulated numerous hypotheses in biogeography, systematics and evolutionary ecology . Many studies have investigated factors that may account for the remarkable number of endemic species occurring in these relatively small geographical areas. For instance, island age and area, environmental heterogeneity and geographical isolation have been pointed out as major factors determining species diversity on islands . However, because most biogeographical models consider total species number, the conclusions drawn from such studies are somewhat biased by the large contribution of those island lineages that experienced dramatic episodes of diversification . Oceanic island floras also harbour a remarkable number of endemic lineages for which variation across populations does not support the occurrence of multiple speciation events . Contrasting levels of diversification among island plant lineages are, in part, probably the result of processes associated with intrinsic traits , which, in addition to ecological opportunity , square plant pots may explain the patterns of diversifi- cation in these areas. Fruit type and growth habit are two life history characters that have been the subject of considerable attention with regard to their relationship with speciation .
Having an herbaceous growth habit may promote diversification rates in plant lineages because of short generation times or high fecundity . High rates of molecular evolution in herbaceous taxa relative to woody plants also support this idea . In contrast, other studies relate woodiness to high species diversity, as woody species may experience lower extinction rates than herbaceous lineages . Fruit type is typically associated with the way in which seeds are most effectively dispersed, which is also expected to affect diversification rates. The frequency and range of seed dispersal may have a significant role in species cohesion, particularly in those species inhabiting areas with strong physical barriers, such as oceanic islands . Fleshy fruits of island species are probably dispersed by frugivorous vertebrates, mostly birds, which may enhance rates of gene flow among populations as a result of frequent consumption and animal mobility. Results from population genetic studies in some fleshy fruited species are apparently congruent with this expectation . Broader comparative studies of the Hawaiian flora, however, indicate that fleshy fruits may favour lineage diversification and high species diversity in some lineages . In this study, we review the recent literature on oceanic island floras to investigate potential associations between life history traits and speciation in island plant lineages. By separating lineages into two contrasting patterns of diversification , we aim to identify those traits more closely related to diversification within archipelagos. We use published phylogenetic reconstructions of ancestral character states to identify which particular traits were predominant among early colonizers that gave rise to species-rich lineages. Species distribution data are also used to infer whether colonization ability could be related to certain trait combinations or type of lineage. Lastly, we review the available molecular evidence to investigate whether fleshy fruits are generally associated with species cohesion in oceanic archipelagos, and consider possible explanations for contrasting levels of diversification of fleshy fruited lineages in different insular settings.Our survey focused on the floras of those oceanic archipelagos for which abundant information from phylogenetic and population genetic studies was available. Archipelagos comprising several islands, not single-island systems, were chosen because multiple islands offer opportunities to analyse the effect of colonization ability on diversification patterns across lineages . In addition, oceanic rather than continental archipelagos were selected because the former generally display a higher diversity of lineages, thus providing robust sample sizes for statistical analysis. The high levels of endemicity on oceanic islands also present ideal circumstances for the analysis of factors related to speciation. It should be noted that, although the selected archipelagos share a number of characteristics useful for our analyses , some other attributes, particularly distance to mainland source areas and climatic conditions, are markedly different. Such differences help to explain the level of endemicity of each archipelago , and provide a good opportunity to investigate whether similar patterns of plant diversi- fication can be found despite geographical differences among archipelagos.During the last two decades, numerous phylogenetic studies have investigated the origin and evolution of oceanic island plant groups that comprise multiple endemics . Population genetic studies at the species level have been comparatively less abundant, although increased accessibility and resolution of molecular markers have led to more studies in recent years . We surveyed 120 published molecular studies and a few complementary taxonomic treatments to extract phylogenetic and population genetic information for lineages of each archipelago . Lineages were established on the basis of current taxonomic and phylogenetic information . In order to analyse differences between contrasting modes of diversification, lineages were classified as ‘speciesrich’ or ‘monotypic’ . Lineages with two extant endemic species were not considered, to ensure that patterns of diversification among types of lineages were markedly different . Lineages with two endemics represent only a small fraction of the total endemic species pool of each archipelago , which means that our analyses covered the endemic flora of each archipelago almost entirely. A few studies have identified some genera for which the pool of species is the result of independent colonization events , and the type and number of lineages in these cases were determined using the most updated taxonomic and molecular information. Recent reviews with a focus on phylogenetic inference on oceanic island lineages were also considered to obtain synthetic information, particularly for Hawai‘i and Galápagos .