Chilling Requirement Validation and Physiological and Molecular Responses of the Bud Endodormancy Release in Paeonia lactiflora ‘Meiju’

The introduction of herbaceous peony (Paeonia lactiflora Pall.) in low-latitude areas is of great significance to expand the landscape application of this world-famous ornamental. With the hazards of climate warming, warm winters occurs frequently, which makes many excellent northern herbaceous peony cultivars unable to meet their chilling requirements (CR) and leads to their poor growth and flowering in southern China. Exploring the endodormancy release mechanism of underground buds is crucial for improving low-CR cultivar screening and breeding. A systematic study was conducted on P. lactiflora ‘Meiju’, a screened cultivar with a typical low-CR trait introduced from northern China, at the morphological, physiological and molecular levels. The CR value of ‘Meiju’ was further verified as 677.5 CUs based on the UT model and morphological observation. As a kind of signal transducer, reactive oxygen species (ROS) released a signal to enter dormancy, which led to corresponding changes in carbohydrate and hormone metabolism in buds, thus promoting underground buds to acquire strong cold resistance and enter endodormancy. The expression of important genes related to ABA metabolism, such as NCED3, PP2C, CBF4 and ABF2, reached peaks at the critical stage of endodormancy release (9 January) and then decreased rapidly; the expression of the GA2ox8 gene related to GA synthesis increased significantly in the early stage of endodormancy release and decreased rapidly after the release of ecodormancy (23 January). Cytological observation showed that the period when the sugar and starch contents decreased and the ABA/GA ratio decreased was when ‘Meiju’ bud endodormancy was released. This study reveals the endodormancy regulation mechanism of ‘Meiju’ buds with the low-CR trait, which lays a theoretical foundation for breeding new herbaceous peony cultivars with the low-CR trait.

Banana Cultivar Field Screening for Resistance to Fusarium oxysporum f.sp. cubense Tropical Race 4 in the Northern Territory

Fusarium oxysporum f.sp. cubense, causal agent of Panama disease, is one of the biggest threats to global banana production, particularly the Cavendish competent tropical race 4 (Foc TR4). It continues to spread globally with detections occurring in regions of the Middle East and new continents such as Africa and South America in the last decade. As the search was on for new management strategies and resistant cultivars to combat the disease, a banana cultivar-screening trial took place in the Northern Territory of Australia, which examined the responses of 24 banana cultivars to the soil borne fungus. These cultivars included material from TBRI, FHIA and selections from Thailand, Indonesia and Australia and evaluated for their resistance to tropical race 4 for two cropping cycles. Several cultivars displayed considerable resistance to Foc TR4, including several FHIA parental lines and hybrids, the Cavendish (AAA) selections GCTCV 215 and GCTCV 247 from TBRI and an Indonesian selection CJ19 showed either very little to no plant death due to the disease.

Developing Production Guidelines for Baby Leaf Hemp (Cannabis sativa L.) as an Edible Salad Green: Cultivar, Sowing Density and Seed Size

Scientific literature is lacking on cultural practices of baby leaf hemp production even though hemp (Cannabis sativa L.) is a widely grown crop for fiber and grain. The objective of this study was to develop a standard protocol to optimize yield and quality of baby leaf hemp production: cultivar screening, sowing density and seed size. Fresh weight (FW) and germination percentage was significantly affected by cultivars. Cultivars ‘Picolo’ and ‘X-59’ had a greater FW mainly due to greater germination percentage. In the sowing density experiment, ‘Ferimon’ and ‘Katani’ were evaluated at five seed densities, 0.65, 1.2, 1.75, 2.3 and 2.85 seeds·cm−2 (42 to 182 seeds per cell). The FW and FW per plant (FWPP) had a positive quadratic response and negative quadratic response, respectively. Regarding seed size, cultivars ‘Anka,’ ‘Ferimon’ and ‘Picolo’ had the largest percentage of seeds, 26% to 30%, within the medium width size between 3.18 and 3.37 mm. Using the largest sized seeds (3.77 mm) increased FW by 34%, 26% and 23% as compared to non-sorted ‘Anka’, ‘Ferimon’ and ‘Picolo’ seeds, respectively. Overall, a greater understanding of cultivar selection, sowing density and seed-size distribution can promote greater yield and quality of baby leaf hemp as an edible salad green.

Screening for susceptibility of Macadamia to E. fornicatus and its fungal symbiont Fusarium euwallaceae.

The polyphagous shothole borer (Euwallacea fornicatus, PSHB), an ambrosia beetle, with its fungal symbiont, Fusarium euwallaceae, is responsible for Fusarium Dieback (FD) in a wide range of woody hosts. In 2019, the first suspected case of E. fornicatus was reported in macadamia in South Africa. The aims of this study were to confirm the E. fornicatus report and thereafter to assess the susceptibility of commercially planted macadamia cultivars to FD caused by F. euwallaceae. The identities of the beetle and associated fungal symbionts were confirmed by means of DNA sequence analysis of the 28S ribosomal large subunit gene for beetles and the internal transcribed spacer region for fungi. Isolates identified as Fusarium species were further characterised by phylogenetic analysis of the translation elongation factor 1α and the β-tubulin gene regions. Thereafter, Koch’s postulates regarding F. euwallaceae were fulfilled on a mature Macadamia integrifolia tree planted at the experimental farm of the University of Pretoria. In order to determine susceptibility against FD, additional cultivar screening was conducted on nine commercially planted cultivars by means of pathogenicity trials using sterilized or inoculated toothpicks inserted into detached branches. Detached branch inoculations showed no significant lesion development six weeks post inoculation, except for cultivar 816. The restricted growth of F. euwallaceae observed in macadamia tissues therefore suggests that macadamia may not be a suitable host for F. euwallaceae and that the threat of FD in macadamia in the event of E. fornicatus infestation is less than for other E. fornicatus hosts. Future work on beetle attraction to macadamia is recommended for a more comprehensive understanding of the interaction between E. fornicatus and its fungal symbionts and macadamia.

Thermography as a Tool to Assess Inter-Cultivar Variability in Garlic Performance along Variations of Soil Water Availability

Climate change entails increasingly frequent, longer, and more severe droughts, especially in some regions, such as the Mediterranean region. Under these water scarcity conditions, agricultural yields of important crops, such as garlic, are threatened. Finding better adapted cultivars to low water availability environments could help mitigate the negative agricultural and economic impacts of climate change. For this purpose, plant phenotyping protocols based on remote-sensing technologies, such as thermal imaging, can be particularly valuable since they facilitate screening and selection of germplasm in a cost-effective manner, covering a wide range of temporal and spatial scales. In this study, the use of a thermal index known as the crop water stress index (CWSI) was tested as a predictor of bulb biomass and for the assessment of inter-cultivar variability of five garlic cultivars in response to a gradient of soil volumetric water contents (VWCs). Three experimental assays, one in the 2018 season and two in 2019, covering a wide range of water availability levels were carried out. Different linear models were developed, with CWSI and VWCs as continuous predictors of bulb biomass, and the factor cultivar as a categorical predictor. The results support the existence of inter-cultivar variation in terms of sensitivity to water availability. The most productive cultivars under favorable conditions were also the most sensitive to water availability. In contrast, the cultivars with lower bulb production potential displayed lower sensitivity to water availability and higher stability across experimental assays. The results also support that CWSI, which was sensitive to inter-cultivar variability, is a good predictor of garlic bulb biomass. Therefore, CWSI can be a valuable tool for garlic phenotyping and cultivar screening.

Wheat and Barley Susceptibility and Tolerance to Multiple Isolates of Wheat streak mosaic virus

One of the greatest virus disease threats to wheat production in the Great Plains of the USA is Wheat streak mosaic virus (WSMV). Breeding programs have developed wheat varieties that are resistant or tolerant to WSMV infection, but these characteristics are climate dependent, and may also vary by WSMV isolate. We tested 10 spring and nine winter wheat (Triticum aestivum) varieties and two barley (Hordeum vulgare) varieties for resistance and tolerance to one WSMV isolate over four years. In spring wheat and barley, there were year by cultivar interactions in terms of resistance and tolerance. However, in winter wheat, yield losses due to WSMV were relatively consistent across years and varieties. Additionally, we tested the impacts of three WSMV isolates individually and in a mixture on twelve, two, and twelve varieties of spring wheat, barley, and winter wheat, respectively. Resistance and tolerance varied by isolate and cultivar, but there were no isolate by cultivar interactions. For spring wheat and barley, yield impacts were greater for two of the three single isolates than for the isolate mixture, whereas in winter wheat, the isolate mixture caused greater yield losses than the individual isolates. Overall, the results indicate that resistance and tolerance phenotypes were influenced by environmental conditions and by WSMV isolate or combination of isolates, suggesting that cultivar screening should be conducted over multiple years and with multiple virus isolates.

The Potential of Common Cereals to form Retrograded Resistant Starch

Resistant starch (RS) has been recognised as a functional fibre with many health-promoting effects. RS exists in four forms – RS₁, RS₂, RS₃, and RS₄. The RS₃type is generated by amylose retrogradation typically resulting from food processing procedures. The aim of this study was to demonstrate the potential ability of six agriculturally important cereals to generate type RS₃resistant starch after retrogradation of their amylose. In comparison with all tested cereals, the statistically significant highest level of RS₃ (5.28% ± 0.68) was detected in triticale, mainly in the Pinokio, Presto, Tricolor, and Kendo cultivars. Significant highly content was also found in rye (4.93% ± 0.73), especially in Selgo, Esprit, Dankowskie Nowe, and Apart cultivars, in comparison with wheat, spring and winter barley, tritordeum and oat. There were unsignificant differences between triticale and rye in RS₃ levels. Wheat contained less RS₃ (3.87% ± 0.55) in comparison to triticale and rye. The best wheats with this trait were the Athlet, Boka, Trane, Versailles, and Torysa cultivars. The content of RS₃ in barley was not high (2.35% ± 0.45 in winter barley, 2.51% ± 0.25 in spring barley), similar to tritordeum (2.26% ± 0.36). The RS₃ content in high amylose barley mutant Glacier was two-fold higher than in other tested barley cultivars (P < 0.01). Only minimal level of RS₃ can be generated from oat seed starch (0.41% ± 0.09). These results indicate that plant species as well as crop cultivar screening are important for the identification of suitable natural sources of resistant starch. Concerning the production of functional foods, it is important to recognize that valuable bread cereals such as wheat and rye are superior sources of this type of dietary fibre and are highly beneficial to the human health. However, it is advisable to continue for other years in these annual results and localities too.  

Development of a Rapid Method Using Oxalic Acid to Assess Resistance Among Hosta Cultivars to Petiole Rot Caused by Sclerotium rolfsii var. delphinii

A rapid assay was developed to assess hosta cultivars for resistance to petiole rot caused by Sclerotium rolfsii var. delphinii. Leaves of greenhouse-grown hosta (Hosta kikutii and Hosta spp. cultivars Munchkin, Lemon Lime, Tardiflora, Pearl Lake, Zounds, Gold Drop, Halcyon, and Honeybells) were treated with 20 ml of oxalic acid (50 mM) on a cotton swab, then incubated at 100% relative humidity and 27°C. After 4 days, incidence of leaves with lesions was evaluated. Cultivars Munchkin, Lemon Lime, and Tardiflora had a relatively high incidence of leaves with lesions, whereas Gold Drop and Halcyon had much lower incidence. These results were generally consistent with those of field and greenhouse cultivar screening tests in which whole plants were inoculated with the pathogen and rated for disease incidence. Additional screening methods, including spray application of either oxalic acid or mycelial fragments of S. rolfsii var. delphinii, were not as repeatable or simple to conduct as the cotton swab assay. The cotton swab method showed potential to accelerate identification of highly resistant hosta cultivars, and thereby aid efforts to breed resistance to petiole rot. Accepted for publication 1 December 2008. Published 28 January 2009.