Colchicine and osmotic stress for improving anther culture efficiency on long grain temperate and tropical japonica rice genotypes

Rapid breeding of an early maturing, high-quality, and high-y.ielding rice cultivar using marker‑assisted selection coupled with optimized anther culture

With the global shift towards healthier eating habits, the focus of the rice industry has evolved from quantity to quality. In China, the Yangtze River Basin is the main area consuming long-grain and high-quality indica rice. Hubei Province, a significant rice-producing area, currently cultivates a limited range of rice varieties, risking degradation and diminishing economic returns. Therefore, it is imperative to cultivate elite rice varieties tailored to the local production conditions and can significantly enhance the added value. This study bred the novel rice cultivar "Runxiangyu", characterized by early maturity, high quality, and high yield. It is a hybrid of Ezhong 5, known for its moderate height and excellent quality, albeit with a long growth period and lack of fragrance, and Yuzhenxiang, renowned for its high quality, short growth period, and fragrance but limited by its tall stature and poor tillering ability. The breeding process utilized optimized anther culture coupled with molecular marker-assisted selection (MAS) and phenotype analysis. In the field, the developed cultivar was 120.9 cm tall and had an entire growth period of 117.5 days, demonstrating moderate disease resistance and excellent heat tolerance. Its grains are fragrant, meeting the national standard of grade two high-quality rice set by the Food Quality Supervision and Inspection Center of the Ministry of Agriculture and Rural Areas). Exhibiting superior agronomic traits, such as plant type, height, growth period, and stress resistance, along with and quality attributes, including grain shape, chalkiness, fragrance, and taste, "Runxiangyu" was certified by the Agricultural Crop Variety Certification Commission of Hubei in 2022. These findings suggested that molecular MAS coupled with optimized anther culture and multi-site phenotype analysis is an efficient and rapid method for crop breeding.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-024-01495-4.

Unveiling the Genetic Basis Underlying Rice Anther Culturability via Segregation Distortion Analysis in Doubled Haploid Population

Anther culture (AC) is a valuable technique in rice breeding. However, the genetic mechanisms underlying anther culturability remain elusive, which has hindered its widespread adoption in rice breeding programs. During AC, microspores carrying favorable alleles for AC are selectively regenerated, leading to segregation distortion (SD) of chromosomal regions linked to these alleles in the doubled haploid (DH) population. Using the AC method, a DH population was generated from the japonica hybrid rice Shenyou 26. A genetic map consisting of 470 SNPs was constructed using this DH population, and SD analysis was performed at both the single- and two-locus levels to dissect the genetic basis underlying anther culturability. Five segregation distortion loci (SDLs) potentially linked to anther culturability were identified. Among these, SDL5 exhibited an overrepresentation of alleles from the female parent, while SDL1.1, SDL1.2, SDL2, and SDL7 displayed an overrepresentation of alleles from the male parent. Furthermore, six pairs of epistatic interactions (EPIs) that influenced two-locus SDs in the DH population were discovered. A cluster of genetic loci, associated with EPI-1, EPI-3, EPI-4, and EPI-5, overlapped with SDL1.1, indicating that the SDL1.1 locus may play a role in regulating anther culturability via both additive and epistatic mechanisms. These findings provide valuable insights into the genetic control of anther culturability in rice and lay the foundation for future research focused on identifying the causal genes associated with anther culturability.

Embryo Rescue in Plant Breeding

Embryo rescue (ER) techniques are among the oldest and most successful in vitro tissue culture protocols used with plant species. ER refers to a series of methods that promote the development of an immature or lethal embryo into a viable plant. Intraspecific, interspecific, or intergeneric crosses allow the introgression of important alleles of agricultural interest from wild species, such as resistance or tolerance to abiotic and biotic stresses or morphological traits in crops. However, pre-zygotic and post-zygotic reproductive barriers often present challenges in achieving successful hybridization. Pre-zygotic barriers manifest as incompatibility reactions that hinder pollen germination, pollen tube growth, or penetration into the ovule occurring in various tissues, such as the stigma, style, or ovary. To overcome these barriers, several strategies are employed, including cut-style or graft-on-style techniques, the utilization of mixed pollen from distinct species, placenta pollination, and in vitro ovule pollination. On the other hand, post-zygotic barriers act at different tissues and stages ranging from early embryo development to the subsequent growth and reproduction of the offspring. Many crosses among different genera result in embryo abortion due to the failure of endosperm development. In such cases, ER techniques are needed to rescue these hybrids. ER holds great promise for not only facilitating successful crosses but also for obtaining haploids, doubled haploids, and manipulating the ploidy levels for chromosome engineering by monosomic and disomic addition as well substitution lines. Furthermore, ER can be used to shorten the reproductive cycle and for the propagation of rare plants. Additionally, it has been repeatedly used to study the stages of embryonic development, especially in embryo-lethal mutants. The most widely used ER procedure is the culture of immature embryos taken and placed directly on culture media. In certain cases, the in vitro culture of ovule, ovaries or placentas enables the successful development of young embryos from the zygote stage to maturity.

Development of In Vitro Anther Culture for Doubled Haploid Plant Production in Indica Rice (Oryza sativa L.) Genotypes

Anther culture is an efficient biotechnological tool in modern plant breeding programs to produce new varieties and parental lines in hybrid seed productions. However, some bottlenecks-low induction rate, genotype dependency, albinism-restrict the widespread utilization of in vitro anther culture in rice breeding, especially in Oryza sativa ssp. indica (indica) genotypes, while an improved efficient protocol can shorten the process of breeding. Three different induction media (N₆NDK_, N₆NDZ, Ali-1) and four plant regeneration media (mMSNBK1, MSNBK3, MSNBKZ1, MSNBKZ2) were tested with five indica rice genotypes to increase the efficiency of in vitro androgenesis (number of calli and regenerated green plantlets). The production of calli was more efficient on the N₆NDK medium with an average 88.26 calli/100 anthers and N₆NDZ medium with an average of 103.88 calli/100 anthers as compared to Ali-1 with an average of 6.96 calli/100 anthers. The production of green plantlets was greater when calli was produced on N₆NDK medium (2.15 green plantlets/100 anthers) compared when produced on to N₆NDZ medium (1.18 green plantlets/100 anthers). Highest green plantlets production (4.7 green plantlets/100 anthers) was achieved when mMSNBK1 plant regeneration medium was used on calli produced utilizing N₆NDK induction medium. In the best overall treatment (N₆NDK induction medium and mMSNBK1 plant regeneration medium), four tested genotypes produced green plantlets. However, the genotype influenced the efficiency, and the green plantlets production ranged from 0.4 green plantlets/100 anthers to 8.4 green plantlets/100 anthers. The ploidy level of 106 acclimatized indica rice plantlets were characterized with flow cytometric analyses to calculate the percentage of spontaneous chromosome doubling. Altogether, 48 haploid-, 55 diploid-, 2 tetraploid- and 1 mixoploid plantlets were identified among the regenerant plantlets, and the spontaneous chromosome doubling percentage was 51.89%. Utilization of DH plants have been integrated as a routine method in the Hungarian rice breeding program. The tetraploid lines can be explored for their potential to offer new scopes for rice research and breeding directions in the future.

Induction of adventitious shoots and tetraploids in Antirrhinum majus L. by treatment of antimitotic agents in vitro without plant growth regulators

We examined the effects of five antimitotic agents using Antirrhinum majus L. 'Maryland True Pink' on the induction of adventitious shoots resulted in increase of frequencies of chromosome doubling without plant growth regulators. Seeds were treated in vitro with 0, 16.5, 32.9, 65.8, 131.6, or 263.2 µM oryzalin (ORY), amiprofos-methyl (APM), butamifos (BUT), or propham (IPC) or 800, 1,600, 3,200, 6,400, or 12,800 µM colchicine (COL) for 7 day. ORY, COL and APM promoted induction of adventitious shoots on the hypocotyls at maximum frequencies of 57.6% with 16.5 µM ORY, 5.6% with 800 µM COL and 88.8% with 131.6 µM APM. ORY and COL also induced adventitious shoots on the epicotyls adjacent to the cotyledons, particularly at high concentrations, with a maximum frequency of 26.0% at 12,800 µM COL. APM treatment increased frequencies of tetraploids from 0.0 to 93.1%, with a positive correlation between the frequency and concentration. By contrast, ORY and COL induced tetraploids at frequencies of 16.0 to 54.6% and 4.0 to 59.4%, respectively, with peaks at both low and high concentrations of each. Correlation analysis revealed that frequencies of adventitious shoot formation could be useful as an index for the induction of tetraploids. These results showed that three of the antimitotic agents tested induced both adventitious shoot and tetraploid without plant growth regulators, indicating that antimitotic action may play a common role in the induction of adventitious shoot.

Species with Haploid or Doubled Haploid Protocols

In this chapter, we present a list of species (and few interspecific hybrids) where haploids and/or doubled haploids have been published, including the method by which they were obtained and the corresponding references. This list is an update of the compilation work of Maluszynski et al. published in 2003, including new species for which protocols were not available at that time, and also novel methodologies developed during these years. The list includes 383 different backgrounds. In this book, we present full protocols to produce DHs in 43 of the species included in this list. In addition, this book includes a chapter for one species not included in the list. This makes a total of 384 species where haploids and/or DHs have been reported up to date.