Identification of QTL Combinations that Cause Spikelet Sterility in Rice Derived from Interspecific Crosses

Background The exploitation of useful genes through interspecific and intersubspecific crosses has been an important strategy for the genetic improvement of rice. Postzygotic reproductive isolation routinely occurs to hinder the growth of pollen or embryo sacs during the reproductive development of the wide crosses. Result In this study, we investigated the genetic relationship between the hybrid breakdown of the population and transferred resistance genes derived from wide crosses using a near-isogenic population composed of 225 lines. Five loci (qSS12, qSS8, qSS11, ePS6-1, and ePS6-2) associated with spikelet fertility (SF) were identified by QTL and epistatic analysis, and two out of five epistasis interactions were found between the three QTLs (qSS12, qSS8 and qSS11) and background marker loci (ePS6-1 and ePS6-2) on chromosome 6. The results of the QTL combinations suggested a genetic model that explains most of the interactions between spikelet fertility and the detected loci with positive or negative effects. Moreover, the major-effect QTLs, qSS12 and qSS8, which exhibited additive gene effects, were narrowed down to 82- and 200-kb regions on chromosomes 12 and 8, respectively. Of the 13 ORFs present in the target regions, Os12g0589400 and Os12g0589898 for qSS12 and OS8g0298700 for qSS8 induced significantly different expression levels of the candidate genes in rice at the young panicle stage. Conclusion The results will be useful for obtaining a further understanding of the mechanism causing the hybrid breakdown of a wide cross and will provide new information for developing rice cultivars with wide compatibility.

Callose depositions underlie the incompatible reaction in intergeneric crosses of rice

Distant hybridization of cereals is often impaired by fertilization barriers. Haploid induction through intergeneric crossing is well developed in wheat but has not been successful in rice due to incompatibility issues. The present study was thus undertaken to identify fertilization barriers that hinder the compatibility of the rice cultivar Punjab Rice 121 with maize and pearl millet lines as pollinators. A total of 37,357 spikelets were pollinated, yielding 494 caryopses upon supplementation with auxins. The resultant caryopses, arising from true intergeneric crosses, lacked embryos. Imaging of the pollinated pistils at different intervals indicated that intense callose depositions block the release of generative nuclei to the ovule in these wide crosses. Rice spikelets pollinated with rice pollen (cis-generic crosses) exhibited positive indicators of fertilization reaction at the micropyle. While the cis-generic crosses initiated true caryopsis formation after 24 h, no comparative reaction was observed in the intergeneric crosses. The current survey underlines that the rice female gametophyte presents a strong pre-fertilization barrier to foreign pollen. This barrier may be modulated in the future by altering genotype and auxin combinations.

Assessing the Suitability of Elite Lines for Hybrid Seed Production and as Testers in Wide Crosses With Wheat Genetic Resources

The use of genetic resources in breeding is considered critical to ensure future selection gain, but the absence of important adaptation genes often masks the breeding value of genetic resources for grain yield. Testing genetic resources in a hybrid background has been proposed as a solution to obtain unbiased estimates of breeding values for grain yield. In our study, we evaluated the suitability of European wheat elite lines for implementing this hybrid strategy, focusing on maximizing seed yield in hybrid production and reducing masking effects due to susceptibility to lodging, yellow rust, and leaf rust of genetic resources. Over a 3-year period, 63 wheat elite female lines were crossed with eight male plant genetic resources in a multi-environment field experiment to evaluate seed yield on the female side. Then, the resulting hybrids and their parents were tested for plant height, lodging, and susceptibility to yellow rust and leaf rust in a further field experiment at multiple locations. We found that seed yield was strongly influenced by the elite wheat line choice in addition to environment and observed substantial differences among elite tester lines in their ability to reduce susceptibility to lodging, yellow rust, and leaf rust when the hybrid strategy was implemented. Consequently, breeders can significantly increase the amount of hybrid seed produced in wide crosses through appropriate tester choice and adapt genetic resources of wheat with the hybrid strategy to the modern cropping system.

Static and Dynamic Testing of Sei Dareh Cable-Stayed Bridge West Sumatera, Indonesia

The Sei Dareh Bridge is a cable-stayed bridge located in West Sumatra Province, Indonesia. The bridge, has a main span of 123 meters length and 9 meters wide, crosses the Batanghari River. Traffic load is transmitted through 4 prestressed cables to a 42.4 meter high pylon made of concrete. Bridge deck and traffic loads are directly supported by steel box girders as main beams that are reinforced laterally with cross beams IWF 800.300.16.24 and stringers IWF 350.350.12.19. This paper discusses static and dynamic testing on the bridge which aims to assess the feasibility before it is opened for public. Based on the test, it was concluded that the 73% static load could not be achieved because the deflection that occurred was beyond the allowable deflection. This is exacerbated by the sound of a loud clanging sound on the ST2-X1 prestressed cable when loading to 240 tons or 58% of the targeted load. In addition, this bridge is included in the "lazy bridge" category because it takes 24 hours to return to an undeformed condition after loading. As a recommendation for this bridge, it is necessary to carry out a structural health monitoring system (SHMS) regularly on the vehicle floor and cables.

Development of Pea Breeding Lines with Resistance to Orobanche crenata Derived from Pea Landraces and Wild Pisum spp.

Pea (Pisum sativum) is an important grain legume worldwide whose cultivation is severely constrained by the root parasitic weed crenate broomrape (Orobanche crenata), which is widespread in the Mediterranean Basin and Middle East. No resistance is available in commercialized cultivars but some levels of incomplete resistance has been reported in pea landraces and Pisum spp. relatives. In this paper we report the development of a number of advanced pea breeding lines with resistance derived from wide crosses with resistant P. fulvum, P. sativum ssp. elatius, P. sativum ssp. syriacum, and with pea landraces, and critically discuss current progress and future perspectives on pea breeding for broomrape resistance. Resistance of breeding lines was confirmed over five field trials, showing markedly reduced broomrape over ground emergence, and in rhizotron experiments, showing either reduced tubercle formation or, in some of the lines, also hampered tubercle development that might grow slower or even become necrotic and die. Breeding lines performed well agronomically, having similar or mostly higher yields than the parental pea cv. Messire in environments with high broomrape incidence.

Negative dominance and dominance-by-dominance epistatic effects reduce grain-yield heterosis in wide crosses in wheat

The genetics underlying heterosis, the difference in performance of crosses compared with midparents, is hypothesized to vary with relatedness between parents. We established a unique germplasm comprising three hybrid wheat sets differing in the degree of divergence between parents and devised a genetic distance measure giving weight to heterotic loci. Heterosis increased steadily with heterotic genetic distance for all 1903 hybrids. Midparent heterosis, however, was significantly lower in the hybrids including crosses between elite and exotic lines than in crosses among elite lines. The analysis of the genetic architecture of heterosis revealed this to be caused by a higher portion of negative dominance and dominance-by-dominance epistatic effects. Collectively, these results expand our understanding of heterosis in crops, an important pillar toward global food security.