A dominant avirulence gene in Orobanche cumana triggers Or5 resistance in sunflower

Orobanche cumana is a weed that grows as a root parasite on sunflower. In general, the O. cumana–sunflower parasitic system is regarded to follow the gene‐for‐gene model, although this has never been demonstrated at the genetic level in O. cumana. The Or5 dominant gene in sunflower confers resistance to O. cumana race E, but not to race F. The objective of this research was to study the inheritance of avirulence/virulence in crosses between plants of O. cumana lines classified as races E and F. Four race E and three race F lines were developed, from which four race E × race F cross‐combinations were made, in three cases including reciprocals. In all cases, F₁ seeds did not have the ability to parasitise sunflower line P‐1380 carrying the Or5 gene, indicating dominance of race E avirulence allele(s). Five F₂ populations comprising a total of 387 F_2:3 families were evaluated on sunflower line P‐1380. In all cases, one‐fourth of the F_2:3 families did not possess the ability to parasitise P‐1380 plants, suggesting that race E avirulence and race F virulence on P‐1380 are allelic and controlled by a single locus. This study demonstrated the gene‐for‐gene interaction in the O. cumana–sunflower parasite system and provided useful information to identify genes involved in O. cumana virulence. The approach followed in this research can contribute to define precisely races of the parasite on the basis of the presence of avirulence genes.     

Identification of cDNAs induced by the organophosphate trichlorphon in the parasitic copepod Lepeophtheirus salmonis (Copepoda; Caligidae)

Lepeophtheirus salmonis is a copepod ectoparasite of wild and farmed salmonids and can cause considerable damage to infected fish. We have examined the effect of the organophosphate trichlorphon, which was one of the early treatments for sea lice as Neguvon^® on L. salmonis. Suppression subtractive hybridisation was used to prepare a cDNA library enriched for cDNAs expressed in response to the organophosphate trichlorophon and using this technique a total of 33 cDNAs were found to be differentially regulated in response to organophosphate exposure. Sequence analysis of the cDNAs revealed that many were involved in cellular stress responses and or neurotoxicity. The expression of two of these cDNAs was confirmed to be up-regulated in response to trichlorophon.     

Genetic diversity and population structure analysis of eight local chicken breeds of Southern Xinjiang

ABSTRACT

1. The genetic diversity and population structure were studied for eight local chicken breeds, including Anjiyan (AN), Hetian Black (HH), Hetian Ma (HM), Aheqi (AH), Baicheng You (BC), Hejing (HJ), Tashkurghan (TS) and Ruoqiang (RQ), in the Southern Xinjiang region of China, using 20 microsatellite markers.

2. Total 336 alleles were obtained from all chicken breeds, with a mean of 16.8 alleles per locus. The polymorphism information content ranged from 0.444 to 0.911, with a mean of 0.729 and almost all of the loci showed significant deviation from Hardy-Weinberg standards. The observed and expected heterozygosity of the eight breeds ranged from 0.5 to 0.677 and from 0.656 to 0.774, with the lowest observed in the AN and the highest in BC breed. The average breed genetic diversity was 0.655 for AN and 0.766 for BC chickens.

3. According to the neighbour-joining (NJ) method, three main clusters were identified in the NJ phylogenetic tree with AN and RQ breeds in one clade, HH and HM breeds in the second clade and TS, HJ, AH and BC breeds in the third clade.

4. Based on STRUCTURE analysis, the most likely cluster number of all breeds was K = 4, whereby HH and HM breeds formed one cluster and AH, BC, HJ and TS formed another, and RQ, AN chicken formed their own distinct cluster. These results indicated that HH and HM breeds had similar genetic background, as did the breeds of AH, BC, HJ and TS. RQ, AN breed had unique genetic backgrounds, distinct from the other breeds. Genetic introgression was detected from AN to HH and HM.

5. The results of the current study can be used as baseline genetic information to implement effective conservation programs and to make better use of these local chicken breeds, especially for the AN, RQ and TS breeds.     

Species hybrids in the genus <Emphasis Type="Italic">Phytophthora</Emphasis> with emphasis on the alder pathogen <Emphasis Type="Italic">Phytophthora alni</Emphasis>: a review

This review provides a summary of recent examples of interspecific hybridisation within the oomycetous genus Phytophthora. Species hybrids either created in the laboratory or evolved in natural environments are discussed in association with evolutionary issues and possible threats they may pose to agriculture, horticulture and forestry. It is suggested that sustainable control of such hybrids will depend on the better understanding of temporal and spatial aspects of genetic mechanisms and environmental factors that lead to the hybridisation process and thus the genetic diversity in Phytophthora populations.     

Germination rates of weedy radish populations (Raphanus spp.) altered by crop‐wild hybridisation,not human‐mediated changes to soil moisture

Cultivated plants are known to readily hybridise with their wild relatives, sometimes forming populations with weedier life‐history strategies than their progenitors. Due to altered precipitation patterns from human‐induced global climate change, crop‐wild hybrid populations may have new and unpredictable environmental tolerances relative to parental populations, which would further challenge farming and land‐management weed control strategies. To recognise the role of seed dormancy variation in weed invasion, we compared seedbank dynamics of two cross‐type populations (wild radish, Raphanus raphanistrum, and crop‐wild hybrid radish, R. raphanistrum × R. sativus) across a soil moisture gradient. In a seed‐burial experiment, we assessed relative rates of seed germination, dormancy and seed mortality over two years across cross types (crop‐wild hybrid or wild) and watering treatments (where water was withheld, equal to annual rainfall, or double annual rainfall). Weekly population censuses in 2012 and 2013 assessed the frequency and timing of seedling emergence within a growing season. Generally, germination rates were two times higher and seed dormancy was 58% lower in hybrid versus wild populations. Surprisingly, experimental soil moisture conditions did not determine seedbank dynamics over time. Yet, seed bank dynamics changed between years, potentially related to different amounts of annual rainfall. Thus, variation in seedbank dynamics may be driven by crop‐wild hybridisation rates and, potentially, annual variation in soil moisture conditions.     

The use of wheat-alien and Aegilops-rye amphiploids for introgression of genetic material to wheat

An introduction of genetic material from rye, Aegilops and Elymus into durum and common wheat by crossing the wheat species with different amphiploids, has been attempted. Meiotic studies of the hybrids demonstrated that the wheat Elymus sibiricus amphiploid contained several (two or three) genes suppressing the activity of the wheat homoeologous pairing control system. Somatic chromosome studies of the hybrids revealed that the distributions of the alien chromosomes transferred to the second hybrid generation did not correspond to random (0.5 + 0.5)^2k and binomial (p + q)^2k distributions. An essential amendment for gamete and zygote viability, allowing the approximation of distributions by binomial equation, is discussed. The preferential E. sibiricus chromosome transmission was observed. The first backcross was found to be a critical stage while using the Aegilops-rye amphiploids for production of wheat introgressive forms. Stabilisation of the somatic karyotype and improvement of the meiotic regularity was observed in a number of generations. The isolation of stable cytological lines in BC₃ was found to be possible. This revised version was published online in August 2006 with corrections to the Cover Date.     

How can natural hybridisation between self‐compatible and self‐incompatible species be bidirectional?

Self‐compatible (SC) plants often deposit pollen on their own stigmas before flowers open. Thus, if we find natural hybrids between a SC species and a closely related self‐incompatible (SI) species, the pollen donor is usually expected to be the SC species. However, in previous studies of naturally occurring mixed populations of invasive Cakile maritima (SI) and Cakile edentula (SC) in Australia, hybridisation was found to have been bidirectional. Here, we explored the floral development of these species in order to test the hypothesis that there might be a short opportunity for pollinators to visit open SC flowers before the self‐pollen is released. Results indicated that both species showed reverse herkogamy during early development, though by the time pollen was ripe the four long anthers always overtopped the stigma; in C. maritima, most of the short anthers remained below the stigma. In both species, ripe, compatible pollen was able to germinate on the stigmatic surface at all stages of floral development. Anther dehiscence commenced earlier in C. edentula and well before flowers opened, in contrast to C. maritima, but the timing of pollen release varied between individual flowers, with a small proportion of uncontaminated stigmas after flowering; therefore, C. edentula can be either pollen recipient or pollen donor when interspecific outcrossing occurs. In summary, our results suggest that the variation between individual flowers of C. edentula contributed to the bidirectional hybridisation despite being a predominant selfer, providing new insights into plant colonisation.     

Hybrids as potential mediators spreading non-native genes: Comparison of survival,growth, and movement among native,introduced and their hybrid salmonids

Comparing multiple fitness components and potential movement of wild hybrids with their parental species is necessary to fully understand the consequences of human-mediated introgression, but studies tracking both parental species and their hybrids at the individual-level are limited. Here, we compared growth, survival and movement of sympatric introduced brook trout (BT: Salvelinus fontinalis) and native white-spotted charr (WSC: S. leucomaenis) with their hybrids (HYB) in a northern Japanese stream, using mark-recapture data (1,087 marked individuals) collected over 4 years (2013–2016). The mark-recapture data with a single cohort showed that HYB had a comparable or even higher growth rate to BT and WSC. In addition, there is no evidence that hybrid survival was lower than both parental species throughout the entire study period. Furthermore, HYB showed high mobility equivalent to WSC, while BT showed the lowest mobility. Although our previous studies have documented the reduction of BT distribution and lowered reproductive success of HYB, non-native genes can pose a threat to native WSC via relatively high survival, growth and/or mobility of HYB.     

Invasions of rainbow trout and brown trout in Japan: A comparison of invasiveness and impact on native species

Many species of salmonids have been stocked into waters outside of their native range. The invasiveness and impact of these species on native species varies depending on their biological traits, and on environmental conditions, such as climate. In Japan, rainbow trout and brown trout, both listed in 100 of the world's worst invasive alien species by the International Union for Conservation of Nature, occur as non-native species. The invasiveness of these two species is thought to be related to seasonal flooding, given flood waters can physically damage fry and prevent population establishment. Rainbow trout have successfully invaded waters in Hokkaido, northern Japan, where the likelihood of flooding is low between June and July, when their fry emerge, but successful invasions are rare in regions south of Hokkaido. Brown trout, however, have successfully invaded waters not only in Hokkaido, but also other regions. Since brown trout have a similar life history to the native white-spotted charr and masu salmon, with fry emerging before the flood season, they are more suited to the Japanese climate than Rainbow trout. Rainbow and brown trout interact with native species in various ways, but a common outcome of these interactions is the displacement of native charr species. Legal regulations of non-native salmonids should be based on understandings of the ecological traits of each invasive species and regional impacts on native species. Given the ongoing nature of climate change, the nature and extent of the effects of rainbow and brown trout on native species might also change.