Sativa Hybrids Research Articles

Aerial and ground-based phenotyping of an alfalfa diversity panel to assess adaptation to a prolonged drought period in a Mediterranean environment of central Chile

Climate change is one of the biggest challenges facing food production worldwide, particularly in Mediterranean climate regions where rainfall has been decreasing and temperature increasing. Alfalfa is a perennial forage crop that could play an important role in increasing the resilience and sustainability of rainfed production systems in these environments. In this study, we tested how a prolonged drought period of 5–6 months in a Mediterranean environment of central Chile affects the plant persistence and productivity of an alfalfa diversity panel of 69 landraces, cultivars, and diverse pre-breeding populations (hereafter accessions) from Kazakhstan, Azerbaijan, Spain, Australia, USA, and Chile, with putative drought tolerance. The objectives were i) to evaluate the phenotypic variability in plant survival and productivity among the alfalfa diversity panel, under rainfed and with supplemental irrigation, in a Mediterranean environment; and ii) to study the use of an NDVI sensor, and RGB and thermal cameras for field phenotyping and evaluation of canopy traits, such as leaf area index (LAI) and forage yield (FY). Results showed large phenotypic variability for plant survival after the three drought periods, ranging from 30 % to 76 % under rainfed conditions and from 48 % to 90 % with supplementary irrigation. The FY during winter was significantly different between cultivars, with more than 4 Mg ha-1 per year in some accessions. The average FY for three growing seasons (2018–2020) ranged between 2.26 and 10.80 Mg ha-1 under rainfed and 3.92–11.14 Mg ha-1 per year with supplementary irrigation. Among the most productive accessions under both water regimes were two populations of the Medicago arborea x sativa hybrid (AF3448 and AF3347), cultivars Genesis and Venus, and the landraces Aragon from Spain and Alta Sierra 2 from Chile. The normalized difference vegetation index (NDVI) showed exponential and positive relationships with the leaf area index (LAI) and FY. RGB images were obtained at 60 cm above the top of the canopy with a digital camera and at 30 m using a drone. The RGB indices “intensity”, a* and greener area obtained from images taken at 60 cm above the top of the canopy, were highly correlated (r = 0.76 – 0.98; P < 0.0001) with the NDVI and FY, under rainfed and with supplementary irrigation in 2019. The RGB indices “saturation”, a* and u* obtained from a drone at 30 m, were also highly correlated (r > 0.73 – 0.94; P < 0.0001) with the NDVI and FY of accessions growing under both water regimens in 2020. The canopy temperature (CT) obtained from thermal images from a drone was higher under the rainfed regime. The stress degree day (SDD), defined as the difference between canopy temperature (Tc) and air temperature (Ta) was negatively related to FY. Under the rainfed regimen, the population AF3348 and cultivars Genesis and Aragon exhibited the lowest SDD and the highest FY.

First report of the fungus Gnomoniopsis smithogilvyi causing cankers on sweet chestnut (Castanea sativa) in Ireland

In autumn 2020 cankers and branch dieback (Figure 1) were found in a five-year-old gene bank plantation of Castanea sativa in Wicklow, Ireland. The planting material had been imported as grafted saplings from the United Kingdom. Isolations were made from the cankers by surface sterilising the outer bark near the cankers with 70% ethanol. Pieces (5 × 5 × 5mm) of woody material were removed and soaked in 2% NaOCl for one minute, followed by two one-minute distilled water washes. After dabbing dry using paper towels the pieces were placed aseptically onto the surface of malt extract agar (MEA; Difco™) and incubated at 21°C in the dark for three weeks. After several days, hyphal tips were taken from the fungal colonies and transferred onto 2% potato dextrose agar (PDA; DifcoTM). DNA was extracted from the mycelium of seven-day old cultures and the ITS region was sequenced using primers ITS5 and ITS4. Gnomoniopsis smithogilvyi (syn. G. castaneae) (Figure 2) was detected. Microscopic observations agreed with the published descriptions of Shuttleworth et al. (2012) and Visentin et al. (2012). The ITS sequences were deposited in GenBank under the accession numbers OM683278 and OM683279. Sixty three-year-old C. sativa saplings were inoculated with either of two G. smithogilvyi isolates, or a control sterile PDA plug (Table 1). After surface sterilising with 70% ethanol, a stem wound was made using a sterile 6 mm cork borer, 10 cm above soil level. A 6 mm mycelial plug of a three-week-old isolate of G. smithogilvyi was placed onto the wound. This was then covered in moist sterilised cotton wool, wrapped in plastic film, and covered by aluminium foil. Control plants were inoculated with sterile PDA plugs. Treatments were randomised and grown outside, between mid-August to mid-November (mean temperature 14.9°C; mean relative humidity 85.5%). After six weeks dark necrotic lesions (Figure 3; Table 1) were observed on all saplings which had been inoculated with G. smithogilvyi isolates, and G. smithogilvyi was re-isolated from all lesions. Gnomoniopsis smithogilvyi caused girdling on numerous saplings (Figure 4). The identity of the reisolated colonies was confirmed as G. smithogilvyi by morphological assessment and ITS sequencing, fulfilling Koch's postulates. All control saplings were found to be asymptomatic, and no G. smithogilvyi was isolated from these (0/8 attempted re-isolations). Gnomoniopsis smithogilvyi causes cankers on C. sativa hybrids in Spain, and on C. sativa in five European countries (Shuttleworth et al., 2016; Lewis et al., 2017; Lione et al., 2019). It also causes chestnut rot in C. sativa in Australia, France, Italy, New Zealand, Portugal and Switzerland (Visentin et al., 2012; Shuttleworth et al., 2016; Coelho & Gouveia, 2021). This is the first report of G. smithogilvyi causing cankers on C. sativa in Ireland. Follow up surveys and tests are planned to fully understand the distribution of G. smithogilvyi in Ireland.

Additive and non-additive genetic parameters for multipurpose traits in a clonally replicated incomplete factorial test of Castanea spp.

Second-year traits of growth, stem form, terminal flushing, and survival were assessed in 1770 ramets from 295 clones of 16 full-sib families of Castanea spp. Additive, dominance, and epistatic genetic variances were estimated in a clonally replicated incomplete 5 × 4 factorial test. Parents of the mating design were selected mainly on their phenotypes for wood quality (Castanea sativa traditional varieties) and their proven resistance to Phytophthora spp. (Asiatic species and Castanea crenata × C. sativa hybrids). Additive genetic variances were estimated to be 1.7–9 times greater than the dominance components. Inferred epistatic variance components showed a significant role in controlling growth traits and branch length. Narrow- and broad-sense heritability estimates showed that terminal flushing date was the most heritable trait, followed by height. The high estimates of half-sib, full-sib, and clonal mean heritabilities for almost all traits suggest that different strategies of backwards and forwards selection could be proposed. The ranking of the breeding values of parents allow us to select the best parents for new crosses and extend the mating design. Favorable genetic correlations were found between growth traits and straightness, so multi-trait selection looks promising. Our results provide the first information on the partitioning of genetic variance in Castanea spp. and a starting point for devising new selection strategies.

Bipolaris eleusines, a potential mycoherbicide candidate for control of barnyardgrass (Echinochloa crus-galli)

An isolate of Bipolaris eleusines was investigated as a potential candidate for biocontrol of barnyardgrass and additional weeds in paddy rice fields and for safety to selected crop species under greenhouse conditions. Barnyardgrass appeared more susceptible at the three-leaf stage than older plants, and disease severity increased as the fungal inoculum increased from 1 × 105 to 1 × 107 conidia/ml when sprayed till run-off. The high application rate caused 73% mortality of barnyardgrass, relative to the non-treated control, but increasing application rate to >1 × 107 conidia/ml did not enhance efficacy (P >.05). This B. eleusines isolate showed no pathogenicity to rice (Oryza sativa spp. indica, O. sativa spp. japonica and an O. sativa hybrid), corn, wheat or any dicot crop species tested while causing slight infection on sorghum and barley. We conclude that B. eleusines, with high efficacy against barnyardgrass and demonstrated safety to rice, is a promising mycoherbicide candidate worthy of further evaluation and development for control of barnyardgrass in paddy rice fields.

Survey of the incidence of chestnut rot in south-eastern Australia

Chestnut rot of Castanea sativa (European chestnut) and C. crenata (Japanese chestnut) × C. sativa hybrids is a significant problem facing the Australian chestnut industry. It affects the chestnut kernel, symptoms occur as pale, medium and dark brown lesions occurring on the endosperm and embryo. Twenty-two orchards in Victoria and New South Wales were surveyed in 2008, and 21 of these were again surveyed in 2009. All 22 orchards were affected by chestnut rot. Incidence at individual orchards up to 72 % was found in 2008, and 35 % in 2009. Incidence varied widely between orchards and within individual orchards between the 2 years. All varieties were affected, including Decoppi Marone, Purton’s Pride and Red Spanish, displaying examples of both high incidence (>1 %) and industry acceptable incidence (0–1 %) depending on orchard and year. In 2008 and 2009, surveys of Sydney Markets showed incidence of >1 % (2008: varieties Decoppi Marone, Purton’s Pride; and in 2009: varieties Purton’s Pride, Red Spanish). The early December flowering Red Spanish had significantly higher average incidence than the early to mid December flowering Decoppi Marone and Purton’s Pride, suggesting that the timing of flowering may be an important factor affecting incidence. There was a mild positive correlation between orchard incidence and December rainfall of the previous year (r2 = 0.4), indicating rainfall during the chestnut flowering period had a mild effect on incidence.

Inbreeding Depression for Fertility and Biomass in Advanced Generations of Inter‐ and Intrasubspecific Hybrids of Tetraploid Alfalfa

ABSTRACTHybrids between Medicago sativa subsp. sativa L. (hereafter “sativa”) and M. sativa subsp. falcata (L.) Arcang. (hereafter “falcata”) often express heterosis for yield. Yield generally declines when hybrids are inbred due to the loss of desirable dominant alleles or epistatic combinations. We hypothesized that inbreeding sativa–falcata hybrids may show more extensive yield loss than intrasubspecific crosses because of the large genetic difference between subspecies. Our objective was to compare fertility in the greenhouse and biomass production in the field of F1 hybrids and their F2 and S1 generations in both intra‐ and intersubspecific crosses. Field experiments including F1, F2, S1, and double‐cross populations were planted in two locations in Iowa in 2003 and evaluated for yield in 2 yr. Sativa × falcata crosses (SFC) showed greater F1 fertility than intrasubspecific crosses, suggesting that the two subspecies have similar chromosome structure. The SFC did not show high‐parent F1 heterosis, probably because of an intensive harvest schedule favoring sativa × sativa hybrids. However, SFC showed greater inbreeding depression in both F2 and S1 generations than intrasubspecific crosses, possibly reflecting a greater loss of favorable complementary gene interactions. These results suggest that selection within each parental population followed by intercrossing to produce population hybrids may be a better way to improve biomass with this germplasm than advancing hybrids into a recurrent selection program.

Gene flow from cultivated rice (Oryza sativa L.) to wild Oryza species (O. rufipogon Griff. and O. nivara Sharma and Shastry) on the Vientiane plain of Laos

Although Asian cultivated rice (Oryza sativa) and its annual (O. nivara) and perennial (O. rufipogon) wild relatives can freely exchange genes under experimental conditions, little is known about gene flow from the cultivated to these two wild species in natural habitats. The area of study was the Vientiane plain of Laos, at the center of the glutinous rice zone. The objectives of this study were (1) to determine the extent of hybridization between rice and its close wild relatives over a large area on the basis of the O. sativa specific traits glutinous endosperm, colorless apiculus and white pericarp; (2) to evaluate the genetic variation in the hybrid plants based on 13 quantitative traits using principal component analysis. Out of 1576 individual plant samples analyzed two hybrid groups were recognized. One hybrid group consisted of O. rufipogon–O. sativa hybrids and represented 10% of wild individual plants analyzed. The other hybrid group was O. nivara–O. sativa hybrids that represented 14% of wild individuals analyzed. These hybrid groups are distinct based on principal component analysis – this is due to both spatial isolation (> 100 m) and reproductive isolation (i.e. differential flowering time). The results indicate that two kinds of gene flow, between (a) O. sativa and O. rufipogon and (b) O. sativa and O. nivara, are occurring throughout the Vientiane plain of Laos.

Introgressive hexaploid oats from the Avena abyssinica (♀) × A. sativa hybrid: performance, grain lipids and proteins.

A fertile hexaploid oat plant was obtained after several generations of selection for seed set and plant type from a colchicine-produced decaploid hybrid, Avena abyssinica(2n = 4x = 28, AABB) × A. sativa (2n = 6x = 42, AACCDD). The selected line proved to be stably fertile and in many characteristics equal or superior to the hexaploid parent. The grain protein fractions showed two qualitative differences from those of the pollen parent and several differences from the maternal parent. The fractionating extraction used was new for oats. The fatty acid composition of grains of the hybrid derivative was similar to that of the pollen parent, but different from that of the maternal parent. The maternal parent (A. abyssinica) had a relatively high 16:0 fatty acid content (ca. 20.5 mol%) compared with the level of the hexaploid parent and the hybrid derivation (ca. 17.5 mol% each) in field-grown grain. However, in grain produced in the greenhouse, the hexaploids had ca. 20.5 mol% of 16:0 fatty acid and a decrease in 18:1 fatty acid, whereas seed of the A. abyssinica parent showed only a slight increase (ca.21.5 mol%) in 16:0 fatty acid. These and other responses statistically significant may be due to adaptation to temperature conditions being wider in the hexaploids than in the East-African A. abyssinica. A new method of grain lipid extraction was introduced and showed good reproducibility. The derived hexaploid oat can be crossed with A. sativa for breeding purposes and due to its early maturity might also have direct use in northern or high-altitude cultivation.

A high frequency of intergenomic mitochondrial recombination and an overall biased segregation of B. campestris or recombined B. campestris mitochondria were found in somatic hybrids made within Brassicaceae

Mitochondrial segregation and rearrangements were studied in regenerated somatic hybrids from seven different species combinations produced using reproducible and uniform methods. The interspecific hybridizations were made between closely or more distantly related species within the Brassicaceae and were exemplified by three intrageneric, two intergeneric and two intertribal species combinations. The intrageneric combinations were represented by Brassica campestris (+) B. oleracea, B. napus (+) B. nigra and B. napus (+) B. juncea (tournefortii) hybrids, the intergeneric combinations by B. napus (+) Raphanus sativus and B. napus (+) Eruca sativa hybrids, and the intertribal combinations by B. napus (+) Thlaspi perfoliatum and B. napus (+) Arabidopsis thaliana hybrids. In each species combination, one of the two mitochondrial genotypes was B. campestris since the B. napus cultivar used in the fusions contained this cytoplasm. Mitochondrial DNA (mtDNA) analyses were performed using DNA hybridization with nine different mitochondrial genes as probes. Among the various species combinations, 43-95% of the hybrids demonstrated mtDNA rearrangements. All examined B. campestris mtDNA regions could undergo intergenomic recombination since hybrid-specific fragments were found for all of the mtDNA probes analysed. Furthermore, hybrids with identical hybrid-specific fragments were found for all probes except cox II and rrn18/rrn5, supporting the suggestion that intergenomic recombination can involve specific sequences. A strong bias of hybrids having new atp A-or atp9-associated fragments observed in the intra- and intergeneric combinations could imply that these regions contain sequences that have a high reiteration number, which gives them a higher probability of recombining. A biased segregation of B. campestris-or B. campestris-like mitochondria was found in all combinations. A different degree of phylogenetic relatedness between the fusion partners did not have a significant influence on mitochondrial segregation in the hybrids in this study.

The Location of Sources of Field Resistance to Bremia lactucae in Wild Lactuca Species

AbstractThirty‐one accessions of four Lactuca species (L. serriola, L. saligna, L. aculeata, L. squarrosa) and one L. serriola×L. sativa hybrid were screened for field resistance to Bremia lactucae. In the L. serriola group, significant differences in the level of field resistance were distinguished. The accessions PI 281876 and PI 253467 were free of infection. Moreover, all L. saligna accessions tested were totally free from disease during three‐year‐investigation.

Interspecific hybrids involving the recently described diploid taxon Avena atlantica

Chromosome pairing affinities of interspecific hybrids involving the newly discovered species Avena atlantica with A. strigosa, A. hirtula, A. prostrata, A. damascena, A. maroccana, and A. sativa are described. The complete and regular chromosome pairing observed in the hybrids involving A. hirtula and A. strigosa confirms the genomic designation to be AsAs. The chromosome pairing in the A. prostrata, A. damascena, A. maroccana, and A. sativa hybrids indicates that A. atlantica is no more closely related to these species than the other members of the AsAs genomic group. Key words: Avena, meiosis, hybridization, phylogeny.

Specificity of Interactions Between Wild Lactuca spp. and Bremia lactucae Isolates from Lactuca serriola

AbstractSpecificity of interactions between eight Lactuca species and 8 Bremia lactucae isolates was studied in seedlings and adult plants of 36 Lactuca accessions plus one L. serriola × L. sativa hybrid. Pathogenicity of the isolates and/or plant susceptibility was expressed by sporulation intensity.A highly compatible relationship was observed in all of L. serriola accession/isolate interactions tested. A differential reaction was found in numerous cases testifying to physiological specialization of the pathogen in a wild pathosystem. Nonspecific nondifferential compatibility (quantitative resistance) can be expected in L. serriola PI 281876. Age dependent resistance (seedlings versus adult plants, and vice versa) and heterogeneity of reactions were also recorded. The comparisonof B. lactucae isolates from L. sativa and L. serriola has shown a significant shift of pathogenicity in favour of L. serriola accessions. A high level of resistance was found in the L. serriola × L. sativa hybrid.The existence of basic incompatibility can be expected in L. saligna and L. virosa as well as in such taxonomically remote species as L. viminea, L. squarrosa and L. biennis. Other taxonomically remote species, i.e. L. dentata and L. alpina, exhibited a compatible reaction, although the reaction of the former was differential. A high level of sporulation was recorded in all accession/isolate interactions of L. alpina.

Occurrence of Erysiphe cichoracearum Perithecia on Wild Lactuca Species

AbstractPerithecia of Erysiphe cichoracearum (powdery mildew) were found on several, but not all, accessions of Lactuca serriola, L. saligna, L. aculeata and L. serriola × L. sativa hybrid. Their occurrence varied between Lactuca species and different accessions of the same species. Perithecia were globular, had a mean diameter of 125.5 μm and contained an average 13–14 asci. Asci had mean dimensions of 55.0 × 26.1 μm and each contained two ascospores which measured an average 17.4 × 10.6 μm. There were however significant differences in the dimensions of spores and other structures obtained from different Lactuca accessions.

Morphology and metaphase chromosome pairing in three Avena hybrids

The chromosome pairing affinities and some morphological comparisons are described between the hybrids Avena longiglumis × A. damascena, A. damascena × A. canariensis, and A. damascena × A. sativa in relation to each other and some previously reported diploid × diploid and diploid × hexaploid hybrids. Genomic affinities in the A. longiglumis × A. damascena and A. damascena × A. sativa hybrids were found to be consistent with similar hybrids reported previously, but the A. damascena × A. canariensis hybrids show a very close cytogenetic relationship.Key words: oats, hexaploid, Avena hybrids, synapsis.