​Studies on Heterotic Trends in Blackgram [Vigna mungo (L.) Hepper] for Yield and Earliness

Background: As blackgram cultivation is majorly spread in rain fed areas, breeding short duration and high yielding blackgram varieties is of profound importance to tackle terminal moisture stress and reap impressive yields by breaking the yield plateau. Hence, the present study was aimed to identify highly heterotic cross combinations for yield and earliness. Methods: Six parents along with 15 F1s were evaluated (rabi, 2019) for seed yield and its component traits along with earliness to estimate the magnitude of heterosis. Result: The cross LBG-752 × TBG-104 exhibited heterosis estimates in desirable direction for yield and earliness. The next best crosses were LBG-752 × PU-31, TU-40 × TBG-104, LBG-752 × TU-40 and IPU-2-43 × TBG-104. Because of its autogamous genetic architecture and biological constraints in large scale economic hybrid seed production, heterosis could be exploited only by isolating the early maturing and high yielding segregants followed by bi-parental or recurrent selection in early segregating generations and single plant selection in subsequent generations that would result in short duration and high yielding blackgram variety that fits well into different ecological niches.

Transcriptome Analysis of Anther Wall Reveals Novel Insights Into the Regulatory Mechanisms Underlying Anther Wall Development in Rice

Rice is an important food staple that is consumed by half of the human population. Therefore, understanding the regulatory mechanism of male fertility in rice can improve production by enhancing the efficiency of hybrid seed production. However, information on the control mechanism of male fertility by anther dehiscence or wall development in rice is very limited. To further understand the regulatory mechanism for anther dehiscence in rice, we carried out transcriptome analysis for two tissues: the anther wall and pollen at the anthesis stage. With the anatomical meta-expression data, in addition to these tissues, the differentially expressed genes (DEGs) between the two tissues were further refined to identify 1,717 pollen-preferred genes and 534 anther wall-preferred genes. A GUS transgenic line and RT-qPCR analysis for anther wall-preferred genes supported the fidelity of our gene candidates for further analysis. The refined DEGs were functionally classified through Gene Ontology (GO) enrichment and MapMan analyses. Through the analysis of cis-acting elements and alternative splicing variants, we also suggest the feature of regulatory sequences in promoter regions for anther wall-preferred expression and provide information of the unique splicing variants in anther walls. Subsequently, it was found that hormone signaling and the resulting transcriptional regulation pathways may play an important role in anther dehiscence and anther wall development. Our result could provide useful insight for future research to broaden the molecular mechanism of anther dehiscence or anther wall development in rice.

The Unstable Restorer-of-Fertility Locus in Pepper (Capsicum Annuum. L) is Delimited to a Genomic Region Containing PPR Genes

The use of cytoplasmic-genic male sterility (CGMS) systems greatly increases the efficiency of hybrid seed production. Although marker development and candidate gene isolation have been performed for the Restorer-of-fertility (Rf) gene in pepper (Capsicum annuum L.), the broad use of CGMS systems has been hampered by the instability of fertility restoration among pepper accessions, especially sweet peppers, due to the widespread presence of the Unstable Restorer-of-fertility (Rfu) locus. Therefore, to investigate the genetic factors controlling unstable fertility restoration in sweet peppers, we developed a segregation population from a cross between a male-sterile line and an Rfu-containing line to examine the inheritance of Rfu. Individuals with unstable restoration vs. sterility segregated at a 3:1 ratio, indicating that a single dominant gene controls unstable fertility restoration. Genetic mapping delimited the Rfu locus to a 479 kb genomic region on chromosome 6 flanked by two markers, which is close to but different from the previously identified Rf-containing region. The Rfu-containing region harbors a pentatricopeptide repeat (PPR) gene, along with 13 other candidate genes. In addition, this region is syntenic to the genomic region containing the largest number of Rf-like PPR genes in tomato. Therefore, the dynamic evolution of PPR genes might be responsible for both the restoration and instability of fertility in pepper. During genetic mapping, we developed various molecular markers, including one that co-segregated with Rfu. These markers showed higher accuracy for genotyping than previously developed markers, pointing to their possible use in marker-assisted breeding of sweet peppers.

Learning of a mimic odor combined with nectar nonsugar compounds enhances honeybee pollination of a commercial crop

The increasing demand on pollination services leads food industry to consider new strategies for management of pollinators to improve their efficiency in agroecosystems. Recently, it was demonstrated that feeding beehives food scented with an odorant mixture mimicking the floral scent of a crop (sunflower mimic, SM) enhanced foraging activity and improved recruitment to the target inflorescences, which led to higher density of bees on the crop and significantly increased yields. Besides, the oral administration of nonsugar compounds (NSC) naturally found in nectars (caffeine and arginine) improved short and long-term olfactory memory retention in conditioned bees under laboratory conditions. To test the effect of offering of SM-scented food supplemented with NSC on honeybees pollinating sunflower for hybrid seed production, in a commercial plantation we fed colonies SM-scented food (control), and SM-scented food supplemented with either caffeine, arginine, or a mixture of both, in field realistic concentrations. Their foraging activity was assessed at the hive and on the crop up to 90 h after treatment, and sunflower yield was estimated prior to harvest. Our field results show that SM + Mix-treated colonies exhibited the highest incoming rates and densities on the crop. Additionally, overall seed mass was significantly higher by 20% on inflorescences close to these colonies than control colonies. Such results suggest that combined NSC potentiate olfactory learning of a mimic floral odor inside the hive, promoting faster colony-level foraging responses and increasing crop production.

Disruption of the bHLH transcription factor Abnormal Tapetum 1 causes male sterility in watermelon

Although male sterility has been identified as a useful trait for hybrid vigor utilization and hybrid seed production, its underlying molecular mechanisms in Cucurbitaceae species are still largely unclear. Here, a spontaneous male-sterile watermelon mutant, Se18, was reported to have abnormal tapetum development, which resulted in completely aborted pollen grains. Map-based cloning demonstrated that the causal gene Citrullus lanatus Abnormal Tapetum 1 (ClATM1) encodes a basic helix-loop-helix (bHLH) transcription factor with a 10-bp deletion and produces a truncated protein without the bHLH interaction and functional (BIF) domain in Se18 plants. qRT–PCR and RNA in situ hybridization showed that ClATM1 is specifically expressed in the tapetum layer and in microsporocytes during stages 6–8a of anther development. The genetic function of ClATM1 in regulating anther development was verified by CRISPR/Cas9-mediated mutagenesis. Moreover, ClATM1 was significantly downregulated in the Se18 mutant, displaying a clear dose effect at the transcriptional level. Subsequent dual-luciferase reporter, β-glucuronidase (GUS) activity, and yeast one-hybrid assays indicated that ClATM1 could activate its own transcriptional expression through promoter binding. Collectively, ClATM1 is the first male sterility gene cloned from watermelon, and its self-regulatory activity provides new insights into the molecular mechanism underlying anther development in plants.

Female flowering lines as the basis for new highly productive F1 zucchini hybrids

Relevance. The modern marrow seed market shows the prospect of creating F1 hybrids that have the maximum return on a high-quality crop. For their successful selection, parental forms with a complex of economically valuable traits and a high combinational ability are required. The most important role is played by the female zucchini maternal lines of flowering type, which allow for hybrid seed production with free pollination and obtain high quality F1 hybrid seeds.Materials and methods. The studies were carried out at of the Krymsk EBS VIR Branch (Russia, Krasnodar Region, Krymsk) in 2019-2021. Variety testing of lines and hybrids was carried out in the open field in the fields of selective crop rotation. The plot area was 5 m2, the experiment was repeated three times.Results. The general combinative ability of parental squash lines was studied, maternal forms with a positive GCA effect on early yield (F5 409-1, F5 409-2) and on total yield (F5 409-1) were identified. A preliminary variety testing of hybrid combinations was carried out in comparison with the standards F1 Belogor and F1 Pascal. The main economically valuable traits have been studied: early maturity, early and general yield, marketability, product attractiveness. F1 hybrids of zucchini were identified, obtained on the basis of maternal forms of the female type of flowering F5 409-1, F5 409-2 in terms of yield (early above 17,7 t/ha and total above 46,7 t/ha), and marketability, more than 83,2%.Conclusions. The high productivity of F1 zucchini hybrids obtained on the basis of maternal forms of the female flowering type F5 409-1, F5 409-2 proves the promising nature of their use in breeding. As a result of two years of study, a hybrid F1 (409-1×305) was isolated, with a complex of economically valuable traits: early yield 19,6 t/ha, total yield 52,6 t/ha, marketability 84,3%, attractive appearance of fruits.

Heterosis and Combining Ability For Floral and Yield Characters in Rice Using Cytoplasmic Male Sterility System

Developing high-yielding rice genotypes has become more urgent to ensure global food security with continuing population growth and the threat of environmental pressures. Cytoplasmic male sterility (CMS) system provides a valuable approach for commercial exploitation of heterosis and producing high-yielding and quality hybrid rice. Three CMS lines and ten diverse restorers were crossed using line × tester mating design. The obtained thirty F1 hybrids and their thirteen parents were evaluated. Yield traits as well as certain floral traits characters that influence the efficiency of crossing and hybrid seed production as duration of floret opening (min), stigma exsertion (mm), stigma length (mm), opening floret angle, and anther length (mm) were assessed. Highly significant variations were detected among parents, crosses, and parents vs. crosses for all the studied traits. The CMS line L2 and the restorer T5 were identified as good combiners for stigma exsertion, stigma length, opining floret angle, and duration of floret opening. Moreover, the hybrids L1×T1, L1×T3, L2×T2, L2×T5, L3×T4, L3×T5, and L3×T9 had positive SCA effects for most floral traits. Besides, the CMS lines L1 and L3 as well as the restorers T1, T2, T3, T6, and T9 proved to be the best general combiners for grain yield and certain contributing traits. The hybrids L1×T1, L1×T5, L1×T7, L2×T3, L2×T4, L2×T5, L2×T10, L3×T1, L3×T2, and L3×T6 displayed positive SCA effects for grain yield and one or more of its attributes. Both additive and non-additive gene effects are involved in the governing inheritance of all evaluated traits. The biochemical variations among the certain evaluated genotypes were further studied. The esterase and peroxidase isozymes were applied for verifying the genetic diversity at the protein level among the used CMS lines, restorers, and their crosses. All the applied isozymes displayed polymorphism for the parents and their crosses. The banding pattern and intensity differences provided accurate results on the reliable variability among the tested genotypes.

QTL Mapping of a Novel Genomic Region Associated with High Out-Crossing Rate Derived from Oryza longistaminata and Development of New CMS Lines in Rice, O. sativa L.

High seed cost due to poor seed yield severely limits the adoption of hybrid rice by farmers. Increasing the out-crossing rate is one of the key strategies to increase hybrid seed production. Out-crossing rate is highly influenced by the size of female floral traits, which capture pollen grains from male donor plants. In the current study, we identified 14 QTLs derived from the perennial wild rice Oryza longistaminata by composite interval mapping for five key floral traits: stigma length (five), style length (three), stigma breadth (two), stigma area (one), and pistil length (three). QTL analysis and correlation studies revealed that these stigma traits were positively correlated and pleiotropic to the stigma length trait. We selected the major-effect QTL qSTGL8.0 conferring long stigma phenotype for further fine mapping and marker-assisted selection. The qSTGL8.0 (~ 3.9 Mb) was fine mapped using newly developed internal markers and was narrowed down to ~ 2.9 Mb size (RM7356–RM256 markers). Further, the flanking markers were validated in a segregating population and in progenies from different genetic backgrounds. The markers PA08-03 and PA08-18 showed the highest co-segregation with the stigma traits. The qSTGL8.0 was introgressed into two cytoplasmic male sterile (CMS) lines, IR58025A and IR68897A, by foreground, background, and trait selection approaches. The qSTGL8.0 introgression lines in CMS backgrounds showed a significantly higher seed setting rate (2.5–3.0-fold) than the original CMS lines in test crosses with their corresponding maintainer lines. The newly identified QTLs especially qSTGL8.0, will be quite useful for increasing out-crossing rate and this will contribute to increase seed production and decrease seed cost.

Mapping and Analysis of a Novel Genic Male Sterility Gene in Watermelon (Citrullus lanatus)

Seed production is critical for watermelon production, which mostly involves first-generation hybrid varieties. However, watermelon hybrid seed production currently requires complex procedures, including artificial isolation and pollination. Therefore, the development and use of a male-sterile system to generate watermelon hybrids can simplify the process. The scarcity of male-sterile watermelon germplasm resources necessitates the use of molecular breeding methods. Unfortunately, the genes responsible for male sterility in watermelon have not been cloned. Thus, the genetic basis of the male sterility remains unknown. In this study, two DNA pools derived from male-sterile and normal plants in the F2 population were used for whole-genome resequencing. The Illumina high-throughput sequencing resulted in 62.99 Gbp clean reads, with a Q30 of 80% after filtering. On the basis of the SNP index association algorithm, eight candidate regions (0.32 Mb) related to specific traits were detected on chromosome 6. Expression pattern analyses and watermelon transformation studies generated preliminary evidence that Cla006625 encodes a pollen-specific leucine-rich repeat protein (ClaPEX1) influencing the male sterility of watermelon. The identification and use of genic male sterility genes will promote watermelon male sterility research and lay the foundation for the efficient application of seed production technology.

Genomic Scan of Male Fertility Restoration Genes in a ‘Gülzow’ Type Hybrid Breeding System of Rye Secale cereale L.)

Efficient and stable restoration of male fertility (Rf) is a prerequisite for large-scale hybrid seed production but remains an inherent issue in the predominant fertility control system of rye (Secale cereale L.). The ‘Gülzow’ (G)-type cytoplasmic male sterility (CMS) system in hybrid rye breeding exhibits a superior Rf. While having received little scientific attention, one major G-type Rf gene has been identified on 4RL (Rfg1) and two minor genes on 3R (Rfg2) and 6R (Rfg3) chromosomes. Here, we report a comprehensive investigation of the genetics underlying restoration of male fertility in a large G-type CMS breeding system using recent advents in rye genomic resources. This includes: (I) genome-wide association studies (GWAS) on G-type germplasm; (II) GWAS on a biparental mapping population; and (III) an RNA sequence study to investigate the expression of genes residing in Rf-associated regions in G-type rye hybrids. Our findings provide compelling evidence of a novel major G-type non-PPR Rf gene on the 3RL chromosome belonging to the mitochondrial transcription termination factor gene family. We provisionally denote the identified novel Rf gene on 3RL RfNOS1. The discovery made in this study is distinct from known P- and C-type systems in rye as well as recognized CMS systems in barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.). We believe this study constitutes a stepping stone towards understanding the restoration of male fertility in the G-type CMS system and potential resources for addressing the inherent issues of the P-type system.