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Emmer is a progenitor of bread wheat and evolved in the Levant together with the yellow rust (YR), powdery mildew (PM) fungi, and a precursor of Zymoseptoria tritici causing Septoria tritici blotch (STB). We performed a genome-wide association mapping for the three disease resistances with 143 cultivated emmer accessions in multi-environmental trials. Significant (P < 0.001) genotypic variation was found with high heritabilities for the resistances to the two biotrophs and a moderate heritability for STB resistance. For YR, PM, and STB severity nine, three, and seven marker-trait associations, respectively, were detected that were significant across all environments. Most of them were of low to moderate effect, but for PM resistance a potentially new major gene was found on chromosome 7AS. Genomic prediction abilities were high throughout for all three resistances (≥ 0.8) and decreased only slightly for YR and PM resistances when the prediction was done for the second year with the first year as training set (≥ 0.7). For STB resistance prediction ability was much lower in this scenario (0.4). Despite this, genomic selection should be advantageous given the large number of small QTLs responsible for quantitative disease resistances. A challenge for the future is to combine these multiple disease resistances with better lodging tolerance and higher grain yield.

Long-lived tree species face a myriad of biotic and abiotic threats over their lifetime, some of the most serious being the presence of non-native diseases or pests capable of killing greater than 95% of trees that are exposed to them. Fortunately, the genetic diversity in many of the affected species also includes some individuals and populations with genetic resistance. Over the last 50 years, applied resistance programs have been undertaken in a range of tree species in the U.S. and resistant parent trees have been selected, tested in seedling inoculation trials and in field trials, selections placed into seed orchards, and the resulting seed used for reforestation and restoration. Both major gene resistance (MGR) and quantitative resistance (QR) have been documented in these resistance programs. However, for each resistance program the question arises whether the resistance will be durable, permitting the species to be used in managed plantations, urban plantings or in native forest restoration over the long-term. Field plantings to-date indicate that in some cases virulence to MGR can arise relatively quickly and QR appears to offer the best opportunity for durability. Ultimately, more time and plantings will be needed to discern if resistance is durable in affected tree species. Changes in climate may alter dynamics that could influence durability of resistance. However, even in the case of virulence to MGR, the pathogen or pest may not spread throughout the range of plantings, and genetic resistance will likely continue to be an invaluable tool for species affected by diseases and pests.

Kernel filling is an important factor that directly affects kernel yield in maize. Based on a Logistic model, the process of kernel filling in maize can be effectively fitted, and the characteristic parameters with biological significance can be estimated. To clarify the genetic mechanism of characteristic parameters of kernel filling in maize, a recombinant inbred line (RIL) population including 208 lines derived from the maize inbred lines DH1M and T877 were evaluated in Nantong in 2015 and in Yangzhou in 2016, respectively. The kernel dry weights of recombinant inbred lines were measured 10, 15, 20, 25, 30, 35, 40, 43, 46, 49, 52, 55, 58 and 61 days after pollination (DAP). A total of 12 characteristic parameters related to kernel filling were estimated in different environments using the Logistic model. These parameters showed abundant phenotypic variation across two environments in the recombinant inbred line population. Some more ideal genotypes were selected through clustering based on BLUP values of characteristic parameters. Genetic analysis indicated that the 12 characteristic parameters conformed to the “major gene plus polygenes” model. The results of two environments were reproduced well. Most of the characteristic parameters related to kernel filling were controlled by two major genes, and a few characteristic parameters were controlled by three or four major genes. In addition, the genetic models of some characteristic parameters differed in the two environments due to interactions between the genes and environments. This study not only laid a foundation for further clarifying the genetic mechanism of maize kernel filling and mapping the related genes but also suggests a new paradigm for dynamic developing traits.

Rice blast, caused by Magnaporthe oryzae, poses a significant threat to rice production. Rice blast susceptibility has been observed in Japanese rice varieties with excellent eating quality. Enhancing blast resistance is essential to ensure minimal use of agricultural chemicals. Two types of blast resistance are observed: True resistance, which is a type of qualitative resistance expressed by a major gene, and field resistance, which is a type of quantitative resistance expressed by multiple micro-acting genes. ‘Resistance collapse’, in which a variety with a true resistance gene becomes diseased by blast fungus races compatible with the resistance gene, has been observed. Varieties carrying blast-resistance genes, such as Pb1 (panicle blast resistance 1), have been developed through DNA marker-assisted selection. In this review, we focus on the Pb1, which expresses strong quantitative resistance to panicle blast and has been widely used in Japan without showing ‘resistance collapse’ for 40 years. Pb1 is an ‘adult plant resistance gene’ that does not exert strong selection pressure on the blast population during the leaf blast stage, thus preventing the selective multiplication of Pb1-compatible blast strains. This epidemiological mechanism prevents ‘resistance collapse’. Interdisciplinary research and breeding are required to sustainably use genes that induce high field resistance.

The fruit diameter (FD), fruit length (FL), fruit peduncle length (FPL), fruit weight (FW) and fruit index (FI, FL/FD) are important quantitative traits in wolfberry fruit, and also one of the most important goals of variety breeding; however, the inheritance of these traits has not been studied to date. In this study, the genetic analysis of these five fruit traits was undertaken for four pairs of F1 hybrid populations (CI, CII, CIII and CIV) using the major gene and polygene mixed inheritance model. The results showed that the five fruit traits exhibited super-parent segregation in four hybrid combinations, and five traits of progeny with abundant genetic diversity. In CII, CIII and CIV, the mid-parental heterosis ratio (RHm%) of FD, FL, FPL and FI was greater than 0 with positive heterosis. FD, FL and FI in CI, CII and CIII were controlled by one pair of additive-dominant major genes (A-1). However, in CIV, FD was controlled by two pairs of additive-dominant alleles (B-6) and FL was best fitted to polygenic control (A-0). In addition, it was found that FPL in CI, CIII and CIV was controlled by one or two pairs of additive-dominant major genes (A-1, B-6, B-1), and FW in CIII and CIV was also controlled by one or two pairs of additive-dominant major gene controls (A-1, B-1). For FD, FPL, FW and FI in CIII and FPL and FW in CII, the major genes heritability was over 50%, indicating that these traits are affected by both genes and the environment, and that the selection of these traits should be considered in later generations due to the large effect of environmental factors. Therefore, this study provides a theoretical basis for QTL mapping and early selection of hybrid breeding of Lycium fruits.

Day-neutral multiflora chrysanthemums can flower throughout the year without being influenced by daylength and have great application value in gardens. Studying heterosis and the genetic basis of important traits in day-neutral chrysanthemums can accelerate the breeding of new cultivars. In this research, a genetic population was constructed by crossing 135 F1 hybrid progeny from the day-neutral chrysanthemum ‘82-81-19’ (female parent) and the late-flowering chrysanthemum ‘388Q-76’ (male parent). Six traits, including abnormal (crown) bud, plant height, plant crown width, budding date, full flowering date, and number of petal layers, were selected for inheritance and heterosis analyses, and a single-generation major gene plus polygene mixed inheritance model was used to perform mixed inheritance analysis on these traits. The results indicated that the six traits were widely segregated in the F1 population, with the coefficient of variation (CV) ranging from 30% to 84%. The phenomena of heterosis and extra-parent segregation existed generally in F1 progeny, and the ratio of heterosis value of mid-parents (RHm) for the six traits was 45.5%, 2%, 2%, 6%, 6%, and −0.3%, respectively. The mixed genetic analysis showed that the abnormal (crown) bud and budding date were fitted to the B-3 model and controlled by two pairs of additive major genes. The plant height and plant crown width were fitted to the A-0 model, and no major gene was detected. The full flowering date was fitted to the A-1 model and was controlled by one pair of major genes. The number of petal layers was fitted to the B-1 model and controlled by two pairs of additive–dominant major genes. The heritabilities of major genes for abnormal bud, budding date, full flowering date, and the number of petal layers were 1.0, 0.9871, 0.7240, and 0.5612, respectively, indicating that these traits were less affected by environmental factors. Using a percentile scoring method, eight day-neutral chrysanthemum genotypes were selected from the hybrid progeny.

The mixed inheritance model involving major genes and polygenes was used to analyze the inheritance of radish flowering time trait in the B1, B2, F1, and F2 generations. Our results showed that flowering time was regulated by two additive-dominant-epistatic major genes and additive-dominant-epistatic polygenes (E-0 model). The major gene heritability estimated for the B1, B2, and F2 generations was 70.48%, 82.80%, and 86.90%, respectively, while the polygene heritability estimated was 0.00, 12.58%, and 8.19%, respectively. These results suggested that the flowering time of radish was regulated by major genes, with polygenes playing only a minor role. In practice, high heritability of major genes is favorable for an efficient selection of B2 and F2 generations during radish breeding. Six hundred twenty-six SSR markers were screened between late-bolting bulk and the early bolting bulk from F2 population. A marker RSS0119 associated to the flowering time trait was obtained, which revealed a high correlation with the flowering time in the F2 population as well as in 59 radish inbred lines (83.61% and 61.02%, respectively). Our findings will be useful for breeding late-bolting varieties.

Societal Impact Statement Damage to white pine forests by white pine blister rust, caused by the non‐native invasive fungal pathogen Cronartium ribicola, is affecting people across western North America. The loss of white pine forests can impact economic opportunities as well as ecosystem and human well‐being. In this paper we quantify the durability, stability, and usability of natural genetic resistance to the disease in two white pine species using long‐term field trials. By combining quantitative genetic resistance breeding programs with data from field validation trials, land managers and policy makers will be able to better ensure healthy forests for the future. Summary Many tree species are susceptible to non‐native pathogens or pests. Their level of susceptibility can be so severe that they are extirpated, and their use for forest restoration or reforestation is curtailed. Programs to find, enhance, and utilize genetic resistance in tree species are underway. Because trees are long‐lived, resistance must be effective for decades to centuries to be useful. Resistance needs to be durable, stable, and present at a useful level. Field plantings provide the best opportunity to assess resistance durability and stability across a range of environments. In this paper we examine the durability and stability of resistance levels, previously identified in seedling screening trials, of two white pine species, Pinus monticola (western white pine) and P. lambertiana (sugar pine) to white pine blister rust, using eight 15 to 20‐year‐old field trials in Oregon and northern California. We found that resistance varies for each host species and in different environments. Major gene resistance (MGR) may have limited utility and the search for resistance should include all types of resistance, as quantitative disease resistance (QDR) appears to be more durable than MGR in the long term at many sites in our study. Our data provide encouragement and support for the use of long‐term field validation studies in combination with quantitative genetic resistance breeding programs. We advocate for an increased use of field trials to ensure that resistance is effective for restoration and recovery against invasive pathogens and pests. Damage to white pine forests by white pine blister rust, caused by the non‐native invasive fungal pathogen Cronartium ribicola, is affecting people across western North America. The loss of white pine forests can impact economic opportunities as well as ecosystem and human well‐being. In this paper we quantify the durability, stability, and usability of natural genetic resistance to the disease in two white pine species using long‐term field trials. By combining quantitative genetic resistance breeding programs with data from field validation trials, land managers, and policy makers will be able to better ensure healthy forests for the future.

Helianthemum oelandicum var. oelandicum is an endemic taxon on the Baltic island of Öland, SE Sweden. Plants can be classified into two morphs: the bristled morph (with bristles and with or without scattered stellate hairs) and the glabrous morph (without bristles and stellate hairs). In crosses between plants assumed to be homozygous for the trait that characterises the phenotypes of the two morphs, offspring in F1 could not be distinguished from the bristled morph. Segregation in F2 did not deviate from the expected 3:1 ratio (bristled morphs/glabrous morphs), indicating one major gene with a dominant allele for the phenotype of the bristled morph and a recessive allele for the phenotype of the glabrous morph. Besides the Mendelian inheritance of presence/absence of hairs, the density of hairs appeared to be further modified by quantitative genes. The frequency of the recessive allele for the phenotype of the glabrous morph varied among local populations and showed a geographical structure, both on local and regional scales. Possible mechanisms behind the spatial variation in indumentum are discussed.

Helianthemum oelandicum var. canescens (Hartm.) Fr. is an endemic taxon with a restricted distribution (less than 10 km²) in the southernmost part of the Baltic island of Öland, SE, Sweden. The taxon varies with respect to stellate hairs. Most plants can be classified into two morphs, the stellated morph (with a dense carpet of stellate hairs on the abaxial surface of the leaves) and the bristled morph (without a carpet of stellate hairs). In crosses between plants assumed to be homozygous for the trait that characterises the phenotypes of the two morphs, F1 offspring was indistinguishable from the bristled morph. Segregation in F2 did not deviate from the expected 3:1 ratio (bristled morph/stellated morph), indicating one major gene with a dominant allele for the phenotype of the bristled morph and a recessive allele for the phenotype of the stellated morph. Besides the Mendelian inheritance of the presence/absence of a whitish cover of stellate hairs, the density of hairs appeared to be further modified by quantitative genes. The frequency of the recessive allele for the phenotype of the stellated morph varied among populations and showed a geographical structure. Possible mechanisms behind the spatial variation in indumentum are discussed.