Ratooning Ability Research Articles

Light condition during grain-filling stage of main crop strongly influences ratooning ability of low-stubble ratoon rice

Compared with high-stubble ratoon rice (RR), low-stubble RR is superior in yield potential, grain quality, and economic benefit. However, the unstable ratooning ability limits the grain yield of low-stubble RR production. Light condition during the grain-filling stage of main crop (GFMC) may be important for rice ratooning. To elucidate the role of light condition during GFMC in affecting ratooning ability, the key response periods, and their underlying mechanisms, field experiments were conducted using two indica cultivars in 2021 and 2022. To create varied light conditions at the canopy base during GFMC, two planting density treatments combining three nitrogen (N) treatments were established in 2021, and three density treatments combining two N treatments and four shading treatments were established in 2022 for the main crop. Light intensity (LI), light quality as reflected by the ratio of red light/far red light (R/FR), and light transmission ratio (LTR) at the canopy base during GFMC and ratooning ability were dramatically altered by N fertilization but not by planting density. With increased N application, LTR, root bleeding rate, and maximum ratooning rate significantly decreased in 2021. In 2022, low N rate increased LI, R/FR, and maximum ratooning rate by 155.7-241.4%, 47.4-65.3%, and 15.6-27.5%, respectively, but reduced missing hill percentage (proportion of hills without regenerated tillers to the total number of hills) by 30.0-62.1% compared with high N rate. The missing hill percentage was negatively correlated with the indices of light condition, while the maximum ratooning rate was positively correlated with them for both cultivars. Root activity and the ratios of abscisic acid (ABA) to cytokinins (CTK), indole-3-acetic acid (IAA), and IAA+CTK could explain the effect of light condition during GFMC on ratooning ability. Shading experiment confirmed the effect of light condition on ratooning ability and further revealed that only shading during middle and late GFMC affected ratooning ability. These findings provide new insights into the regulation of ratooning ability, which are useful for developing management practices to increase the grain yield and yield stability of low-stubble RR.

In Planta Androgenesis (Paternal Origin) in Saacharum X Erianthus Intergeneric Hybrid

The present investigation was carried in crosses made between Saccharum species hybrid clones i.e. Co 419, Co 7201 and Co 7224 (2n = 108-112) and Erianthus arundinaceus viz. IK 76-91 (2n = 60) and IK 76-99 (2n = 60) for introducing better ratoon ability, vigour, wide ecological adaptability, extensive root system, drought and water logging resistance, high biomass and disease resistance into modern sugarcane cultivars during 2020-23 at VSI-Sugarcane Breeding Centre, Amboli. Parental apomixis (paternal origin) has been recently noticed and it is unique in Saccharum X Erianthus intergeneric cross seedlings. A total of fifty-one seedlings were obtained from above three intergeneric crosses and out of these eighteen seedlings were reported as androgenetic seedlings as the female act as a surrogate mother. At the early stages, seed germination of seedlings was found two types i.e., one type resembling Saccharum and other resembling Erianthus with deep purple coloration. Morphologically androgenetic seedlings were similar to the male parents IK 76-91 and IK 76-99 with tall large tufted grass like clumps, vegetative stem with thick reproductive buds, root zone narrow and only one row of root eyes, the lamina gradually passes into leaf sheath with no auricle and dewlaps. Cytological studies were made in these seedlings and during metaphase the somatic chromosome number was observed to be 2n = 60 rather than expected 2n = 84-90. This paternal origin may be due to the ability of Erianthus male gametes to produce an embryo within the seed tissues of Saccharum species hybrids but without genetic contribution of the seed. Thus, in planta androgenesis is achieved through the combination of embryogenic behavior of male gametes which has entered in the ovule and the ability of ovules to act as a surrogate mother. They could derive either from the fusion of two male gametes or from the early natural diplodization of the haploid embryo. Such homozygous true breeding seedlings of Saccharum X Erianthus with hybrid vigour are extremely important in crop improvement. This system provides an unparalleled opportunity to shorten the breeding cycle and fix agronomic traits in the homozygous state. These androgenetic plants with Saccharum cytoplasm and Erianthus genome are male sterile making them highly useful for further hybridization and sugarcane improvement programme.

Sugarcane (saccharum officinarum L.) traits associated with ratooning ability

ABSTRACT Indirect selection for yield in sugarcane (Saccharum officinarum L.) production can be achieved by identifying and selecting for plant traits that are correlated to yield. This study aimed to identify and quantify sugarcane traits that are associated with ratooning ability to generate information for varieties’ selection. Data sourced from three variety trials established at three sites, comprising eight varieties, and collected over six successive crops (plant cane and five ratoons) were used for this study. The data were subjected to linear mixed model, Spearman’s correlation, and biplot analyses. Stalk height, stalk population, stalk mass, and stalk sucrose mass were significantly correlated with cane and sucrose yield across all ratoon crops, suggesting that varieties that combine these traits over multiple crops will have higher ratoon cane and sucrose yields. Significant correlation between brix and sucrose content suggested that brix can be used to indirectly select for sucrose content. Measuring brix is easier, cheaper, and faster than measuring sucrose content. Significant site and variety effects on ratoon crop yields indicated the existence of opportunities to identify good ratooning varieties that are specifically and or broadly adapted to different growing conditions.

The release of ‘LCP 85‐384’ and its contribution to the Louisiana sugar industry

AbstractBasic breeding efforts initiated at the USDA‐ARS in Houma, LA, in the late 1950s allowed Louisiana sugarcane breeders, once again, to cross with the wild germplasm of cultivated sugarcane, Sacharum spontaneum. ‘LCP 85‐384’ was the first success story from this effort and was quickly adopted by growers. It became clear that the cultivar would prove to be substantially impactful to the Louisiana sugar industry. Performing at unprecedented yields in ratoon crops, LCP 85‐384 changed how Louisiana growers would manage their crops. The variety proved to possess traits that fared well in the subtropical production zones of the state. Substantial stalk populations seemed to play a vital role in the necessary ratoon ability and consequent cold tolerance necessary for production in Louisiana. After significant disease pressure, the variety quickly declined in production acreage, but not in impact. It continued to provide sustained progress as a parent for years, contributing to most modern commercial cultivars in Louisiana. Today, LCP 85‐384 and its progeny are used in breeding and genetic research to usher in the next era of progress in the Louisiana sugar industry. Meanwhile, through cooperative efforts of breeding programs around the world, it is making its mark on the sugarcane industries of Argentina in much the same way as it did in Louisiana. In the future, it is expected that the progress made in the breeding program will continue by building upon the gains achieved from LCP 85‐384 and its progeny for the sustained success of the Louisiana sugarcane industry.

Deciphering Winter Sprouting Potential of Erianthus procerus Derived Sugarcane Hybrids under Subtropical Climates.

Winter sprouting potential and red rot resistance are two key parameters for successful sugarcane breeding in the subtropics. However, the cultivated sugarcane hybrids had a narrow genetic base; hence, the present study was planned to evaluate the Erianthus procerus genome introgressed Saccharum hybrids for their ratooning potential under subtropical climates and red rot tolerance under tropical and subtropical climates. A set of 15 Erianthus procerus derived hybrids confirmed through the 5S rDNA marker, along with five check varieties, were evaluated for agro-morphological, quality, and physiological traits for two years (2018-2019 and 2019-2020) and winter sprouting potential for three years (2018-2019, 2019-2020, and 2020-2021). The experimental material was also tested against the most prevalent isolates of the red rot pathogen in tropical (Cf671 and Cf671 + Cf9401) and subtropical regions (Cf08 and Cf09). The E. procerus hybrid GU 12-19 had the highest winter sprouting potential, with a winter sprouting index (WSI) of 10.6, followed by GU 12-22 with a WSI of 8.5. The other top-performing hybrids were as follows: GU 12-21 and GU 12-29 with a WSI of 7.2 and 6.9, respectively. A set of nine E. procerus-derived hybrids, i.e., GU04 (28) EO-2, GU12-19, GU12-21, GU12-22, GU12-23, GU12-26, GU12-27, GU12-30, and GU12-31, were resistant to the most prevalent isolates of red rot in both tropical and subtropical conditions. The association analysis revealed significant correlations between the various traits, particularly the fibre content, with a maximum number of associations, which indicates its multifaceted impact on sugarcane characteristics. Principal component analysis (PCA) summarised the data, explaining 57.6% of the total variation for the measured traits and genotypes, providing valuable insights into the performance and characteristics of the Erianthus procerus derived hybrids under subtropical climates. The anthocyanin content of Erianthus procerus hybrids was better than the check varieties, ranging from 0.123 to 0.179 (2018-2019) and 0.111 to 0.172 (2019-2020); anthocyanin plays a vital role in mitigating cold injury, acting as an antioxidant in cool weather conditions, particularly in sugarcane. Seven hybrids recorded a more than 22% fibre threshold, indicating their industrial potential. These hybrids could serve as potential donors for cold tolerance and a high ratooning ability, along with red rot resistance, under subtropical climates.

Mowing and nitrogen management guidelines for superior rice ratoon yields

Forage-grain ratoon rice (FG-RR) is a dual-cropping system, with forage harvested in the initial season and grain during the regeneration phase. While it is known that the timing of mowing and nitrogen (N) fertilization are key drivers that influence FG-RR production, physiological mechanisms ensuing mowing and N fertilizer application remain unclear. We conducted field experiments in 2021 and 2022 to investigate the yield and growth characteristics of ratooned crops (RC) under various mowing treatments (heading, milk-ripening, dry-ripening and maturity) using three N levels (135, 270, and 405 kg ha−1), two rice genotypes, Taoyouxiangzhan (TYXZ) and Liangyou 6326 (LY6326). Our results demonstrate a significant increase in ratoon yield when mowing occurred at heading or milk-ripening stages compared with maturity, with a yield increase of 2.2-fold when mowing occurred at heading. Early mowing stages increased stubble biomass (up to 73 %) and non-structural carbohydrate (up to 198 %) compared with that at maturity. Mowing at heading or milk-ripening improved accumulated temperature and light exposure, and when coupled with higher N application (270 kg ha−1 N), amplified ratoon ability to recover. Collectively, these factors raised leaf area index, canopy light interception and biomass. Hierarchical partitioning analysis underscored the substantial yet indirect influence of environmental drivers of ratoon yield, alongside a direct driver of growth, particularly thermal sum. We conclude that mowing at heading and milk-ripening with 270 kg ha−1 N elicits optimal ratoon yield with forage production, although further studies are required to determine how these guidelines vary across environments.

Indices for measuring ratooning ability of sugarcane varieties

AbstractThe primary objective of sugarcane (Saccharum spp.) variety testing programs is to identify cultivars that have high cane yields and good ratooning ability (RA). The purpose of this study was to evaluate the usefulness of six RA indices to estimate RA among sugarcane varieties and to identify an index well suited to predict RA in long‐term ratoon crop cycles. The six indices were as follows: ratoon crops yield means, second ratoon to plant cane yield ratio, final ratoon crop to plant cane yield ratio, mean of ratoon crops to plant cane yield ratio (RP), linear regression, and quadratic regression. Data from four variety trials consisting of eight post‐release varieties plus a control, harvested early, mid, and late in the cropping season for over six crop cycles, were used to estimate the RA indices. To identify indices that can predict RA in long‐term ratoon crop cycles, simple linear regression analyses were used to compare the RA indices derived from 6‐year crop cycles and similar indices derived from data from 111 commercial fields harvested over 11 successive crops. Coefficient of determination (R2) values plotted against their respective ratoon crop numbers were used to determine the minimum number of ratoon crops required to accurately predict RA indices for the 11‐year crop cycle. The six indices varied in their rankings of the RA of varieties, emphasizing the importance of identifying the most appropriate indices for different ratooning practices. Based on its highest R2 value of 0.92, the RP index was identified as the most accurate index to predict RA in long‐term ratoon crop cycles requiring a minimum of five successive crops.

Partial factor productivity and water use efficiency of ratoon pigeonpea under varied levels of irrigation, fertigation, and mulching

The scarcity of irrigation water and nutrients poses a serious challenge to the production of pigeonpea in the changing climate. Despite largest producer of pigeonpea, India is still not meeting the domestic pulses requirement. Exploiting the ratoon ability of pigeonpea in rainy and post-rainy seasons would produce higher grains with limited resources in shorter periods due to multiple harvests. Therefore, the present study was conducted to know the resource requirement of ratoon pigeonpea, partial factor productivity (PFP), and water use efficiency (WUE). Two irrigation levels (I 1= 0.50 and I 2=0.75 Crop Pan Evaporation), three nutrient levels (F 1 = 100%, F 2 = 75%, and F 3 = 50% of recommended dose of fertilizers; 25:50:25 kg N:P2O5:K2O ha−1) and two mulching levels (M 0 = without mulching, and M 1 = with mulching) were laid out in split-split plot design at University of Agricultural Sciences, GKVK, Bengaluru. Results revealed that a combination (I 2 F 1 M 1) of a higher level of irrigation (0.75 CPE) and 100% of recommended fertilizer through fertigation with mulching produced higher dry matter accumulation (190.16 g plant−1 at harvest) and nutrients (82.08, 17.37, and 78.35 kg total N, P, and K ha−1, respectively) uptake. Whereas, higher PFP of nutrients (58.12, 29.06, and 58.12 kg grain kg−1 of N, P, and K fertilizer nutrient, respectively) and WUE (21.07 kg ha-cm−1) were observed in higher irrigation with 50% of required fertilizer and mulching (I 1 F 3 M 1) as a result of higher yield and lesser resources used. Therefore, a concurrent supply of optimum irrigation and mulching could improve the PFP and WUE of ratoon pigeonpea even under reduced fertilizer application.

The general ratooning ability of rice yield‐related traits: A meta‐analysis

AbstractNumerous studies have attempted to pinpoint certain traits of rice varieties linked with great ratooning ability that may be used in cultural practice. However, both genetic and environmental variables affect rice's capacity for ratooning. We are able to measure the innovative ratooning ability that affects the decline in ratoon yield using the agronomic features of the main crop and ratoon rice in our global database for a meta‐analysis, drawn from 51 experiments in 14 countries. We discovered that changes in cultivar yield and maturity features, cropping location, and nitrogen fertilizer treatment may all affect a plant's capacity to tiller. On the other hand, the growth duration ratoon ability was less responsive to variations in cultivars and cropping location. We also found that ratooning changes the plant architecture for yield generation from bigger spikelets with fewer panicles to fewer spikelets (dropping 48%) with larger panicles (increasing 19%). We came to the conclusion based on our research that the decreased yield in ratoon crops may be caused by fast ear emergence and aggressive tillering, which negatively influence stem elongation, panicle differentiation, and a lack of nutrition, resulting in fewer spikelets (panicle−1). The present data are thoroughly summarized and analyzed in this research, which also clarifies the lack of knowledge around the characteristics that affect ratoon rice crop production.

Impact of soil type and harvest season on the ratooning ability of sugarcane varieties

Summary Sugarcane varieties differ in their ratooning ability (RA), and it is hypothesized that soil types and harvest seasons impact varieties’ RA. However, the effects of these factors on varieties’ RA remain unclear. This study aimed to assess the RA of different commercial sugarcane varieties (NCo376, N19, N23, N25, and N36), and establish the effects of soils and seasons on ratoon yields of these varieties in Eswatini. Fifteen years data on tons cane per ha per annum (TCHA) and tons sucrose per ha per annum (TSHA) achieved by plant cane and seven ratoon crops were collected from four commercial growers and analysed using linear regression models. The varieties significantly differed in RA. Variety N25, which had the highest plant cane yields (121.3 TCHA and 16.7 TSHA), had the sharpest yield decline over ratoon crops (–2.74 TCHA and −0.33 TSHA), suggesting that this variety is more suitable for short crop cycles. Variety N36 had second highest plant cane yields (111.7 TCHA and 16.4 TSHA) and a lower ratoon yield decline (–1.38 TCHA and −0.16 TSHA) than N25, suggesting that it is suitable for longer ratoon crop cycles. While soil type and harvest season significantly affected the relative yields of varieties, they did not significantly impact their RA, indicating that differences in varieties’ RA were driven by genotype and were relatively stable across environments. This suggests that tests to assess the adaptability of varieties should be conducted in multiple environments, while testing the RA of varieties may be conducted in fewer environments.

Control of rice ratooning ability by a nucleoredoxin that inhibits histidine kinase dimerization to attenuate cytokinin signaling in axillary buds

Rice ratooning, the fast outgrowth of dormant buds on stubble, is an important cropping practice in rice production. However, the low ratooning ability (RA) of most rice varieties restricts the application of this cost-efficient system, and the genetic basis of RA remains unknown. In this study, we dissected the genetic architecture of RA by a genome-wide association study in a natural rice population. Rice ratooning ability 3 (RRA3), encoding a hitherto not characterized nucleoredoxin involved in reduction of disulfide bonds, was identified as the causal gene of a major locus controlling RA. Overexpression of RRA3 in rice significantly accelerated leaf senescence and reduced RA, whereas knockout of RRA3 significantly delayed leaf senescence and increased RA and ratoon yield. We demonstrated that RRA3 interacts with Oryza sativa histidine kinase 4 (OHK4), a cytokinin receptor, and inhibits the dimerization of OHK4 through disulfide bond reduction. This inhibition ultimately led to decreased cytokinin signaling and reduced RA. In addition, variations in the RRA3 promoter were identified to be associated with RA. Introgression of a superior haplotype with weak expression of RRA3 into the elite rice variety Guichao 2 significantly increased RA and ratoon yield by 23.8%. Collectively, this study not only uncovers an undocumented regulatory mechanism of cytokinin signaling through de-dimerization of a histidine kinase receptor—but also provides an eximious gene with promising value for ratoon rice breeding.

Predicting Ratooning Ability of Sugarcane Varieties in Selection Trials

Predicting Ratooning Ability of Sugarcane Varieties in Selection Trials

Investigation on the forage utilization of indica and japonica weedy rice with strong ratooning ability

AbstractThere was few research on the utilization and development of weedy rice. Some weedy rice has remarkable good characteristics as forage in some soil which is difficult to plant crops and pastures. In this study, two weedy rice lines of japonica and indica subspecies with high ratooning ability (Xijing, japonica; Gaoxian, indica) were used to study the possibility of their forage utilization and related suitable cultivation methods. Three different stubble heights of first season were set in 2018 and 2019, and three cutting times of first season (heading stage, milk stage, and waxy ripening stage) were set in 2019. The ratoon grass was harvested 40 days after the first season harvest. For japonica weedy rice line Xijing, its grass yield was significantly lower than that of indica weedy rice line Gaoxian. The dry matter yield of first season grass plus ratoon grass of Gaoxian with the first season harvested at milk stage was the highest of all. The total digestible dry matter yield (first season grass plus ratoon grass) of Gaoxian with 15 cm cutting stubble of first season was higher than those of stubble 30 and 45 cm treatments (p < .05). In conclusions, indica weedy rice line Gaoxian, with high biomass of first season and good ratooning ability, had the good potential for forage development by harvesting first season at milk stage with 15 cm stubble height.

A first look at the ability to use genomic prediction for improving the ratooning ability of sugarcane.

The sugarcane ratooning ability (RA) is the most important target trait for breeders seeking to enhance the profitability of sugarcane production by reducing the planting cost. Understanding the genetics governing the RA could help breeders by identifying molecular markers that could be used for genomics-assisted breeding (GAB). A replicated field trial was conducted for three crop cycles (plant cane, first ratoon, and second ratoon) using 432 sugarcane clones and used for conducting genome-wide association and genomic prediction of five sugar and yield component traits of the RA. The RA traits for economic index (EI), stalk population (SP), stalk weight (SW), tonns of cane per hectare (TCH), and tonns of sucrose per hectare (TSH) were estimated from the yield and sugar data. A total of six putative quantitative trait loci and eight nonredundant single-nucleotide polymorphism (SNP) markers were associated with all five tested RA traits and appear to be unique. Seven putative candidate genes were colocated with significant SNPs associated with the five RA traits. The genomic prediction accuracies for those tested traits were moderate and ranged from 0.21 to 0.36. However, the models fitting fixed effects for the most significant associated markers for each respective trait did not give any advantages over the standard models without fixed effects. As a result of this study, more robust markers could be used in the future for clone selection in sugarcane, potentially helping resolve the genetic control of the RA in sugarcane.

Selection of New Sugarcane Genotypes for Sandy Soils in Florida with Enhanced Sucrose Content

The selection of sugarcane genotypes with high sucrose content and good ratooning ability (RA) is an important objective of the Canal Point breeding program to improve the current profitability levels of the Florida sugarcane industry. In this study, thirteen test sugarcane genotypes and three checks were evaluated in three sand locations, Pahokee Produce Inc. (PP), Townsite farm (TS), and Lykes Brothers Inc. (PF), during three crop cycles (plant cane, first ratoon, and second ratoon). Multi-environment best linear unbiased predictors (BLUPs) were highly significant for commercially recoverable sucrose (CRS) and not significant for cane yield (CY) among genotypes. The ANOVA based on the RA values produced significant genotypic effects but a reduced RA diversity among the genotypes. The simultaneous selection for BLUP_CRS, BLUP_CY yield, and RA identified CP 14-4165 and CP 13-2340 as the most outstanding genotypes. The BLUP_GGE biplots method showed that the PP location was the most discriminative for BLUP_CY, whereas the TS was the ideal location. For BLUP_CRS, the three locations had similar abilities to discriminate genotypes and were positively and strongly correlated. The which-won-where graph indicated that CP 13-2340 showed the highest BLUP_CRS levels in TS and PP locations, while CP 14-4165 and CP 14-4588 were the top genotypes in the PF location. The results suggest that selecting genotypes with high CRS values is possible without compromising the genotype discrimination for CY. CP 14-4165 and CP 13-2340 are resistant to most diseases and genetically diverse.

Yield component evaluation of mutated sugarcane at first and ratooning plantations

Increasing national sugar production can be done by developing new varieties of sugarcane varieties with high potential yields. To ensure profitability and sustainability, however, the new varieties should be accompanied by data on their ratooning ability. This study aimed to evaluate the stability of the yield component of ratooning sugarcane resulting from mutations. The experiment was arranged using a factorial randomized complete block design with the first factor being four genotypes of sugarcane (G) consisting of three mutant genotypes with codes M3.2, M3.3, M3.4 and one original Bululawang genotype (BL). The second factor was ratooning (K) which consisted of three levels, namely first plant (TP), first ratoon (TK1) and second ratoon (TK2). The combination of treatments was repeated 4 times so that 48 unit combinations were obtained. One unit consisted of 28 cane clumps divided into 4 rows. The results showed that the ratooning factor had a significant impact on the value of the proportion of sucrose produced by the mutant sugar cane genotype. The ratooning ability of mutant genotypes to produce sucrose was recorded above 75%. All genotypes of mutant had superior characters compared to non-mutant based on stalk weight and percentage of sucrose.
 Keywords: Bululawang, morphology, mutant, ratoon, sugar

Mapping of QTLs and Screening Candidate Genes Associated with the Ability of Sugarcane Tillering and Ratooning.

The processes of sugarcane tillering and ratooning, which directly affect the yield of plant cane and ratoon, are of vital importance to the population establishment and the effective stalk number per unit area. In the present study, the phenotypic data of 285 F1 progenies from a cross of sugarcane varieties YT93-159 × ROC22 were collected in eight environments, which consisted of plant cane and ratoon cultivated in three different ecological sites. The broad sense heritability (H2) of the tillering and the ratoon sprouting was 0.64 and 0.63, respectively, indicating that they were middle to middle-high heritable traits, and there is a significantly positive correlation between the two traits. Furthermore, a total of 26 quantitative trait loci (QTLs) related to the tillering ability and 11 QTLs associated with the ratooning ability were mapped on two high-quality genetic maps derived from a 100K SNP chip, and their phenotypic variance explained (PVE) ranged from 4.27-25.70% and 6.20-13.54%, respectively. Among them, four consistent QTLs of qPCTR-R9, qPCTR-Y28, qPCTR-Y60/qRSR-Y60 and PCTR-Y8-1/qRSR-Y8 were mapped in two environments, of which, qPCTR-Y8-1/qRSR-Y8 had the PVEs of 11.90% in the plant cane and 7.88% in the ratoon. Furthermore, a total of 25 candidate genes were identified in the interval of the above four consistent QTLs and four major QTLs of qPCTR-Y8-1, qPCTR-Y8-2, qRSR-R51 and qRSR-Y43-2, with the PVEs from 11.73-25.70%. All these genes were associated with tillering, including eight transcription factors (TFs), while 15 of them were associated with ratooning, of which there were five TFs. These QTLs and genes can provide a scientific reference for genetic improvement of tillering and ratooning traits in sugarcane.

Crossability analysis of cultivated rice (Oryza sativa) with O. rufipogon and O. longistaminata and F1-identification

The research was conducted at Instructional cum Research (ICR) farm in Assam Agricultural University, Jorhat, Assam for the year 2019–21 with the objective to determine the crossability of wild rice species O. longistaminata and O. rufipogon with O. sativa and observe the inheritance of rhizome. In first year of experiment, varieties having good ratooning ability were identified. Out of them, five varieties namely Ranjit, Ranjit sub-1, IR-64, Binadhan-11 and Bahadur were crossed with both of the wild species. Crossablity of O. longistaminata with O. sativa ranged from 11.1% (Ranjit sub-1 × O. longistaminata) to 22.2% (Binadhan11 × O. longistaminata) while O. rufipogon with O. sativa ranged from 13.3% (Ranjit sub-1 × O. rufipogon) to 30% (Ranjit × O. rufipogon). All the hybrids except for IR64 × O. longistaminata were photoinsensitive as that of their female parent. Hybrids from O. sativa/O. longistaminata exhibited various distinguishing characters which can be used as morphological marker in order to identify true interspecific hybrids in further breeding programme. The pollen viability of these interspecific hybrids were found lower than both the parents. However, rhizome formation could not be observed in any hybrid.

Fine Mapping and Cloning of a qRA2 Affect the Ratooning Ability in Rice (Oryza sativa L.).

Ratooning ability is a key factor that influences the ratoon rice yield in areas where light and temperature are not sufficient for second-season rice. Near-isogenic lines (NILs) are the most powerful tools for the detection and precise mapping of quantitative trait loci (QTLs). In this study, using 176 NILs, we identified a novel QTL for ratooning ability in NIL128. First, we mapped the QTL between the markers Indel12-29 and Indel12-31, which encompass a region of 233 kb. The rice genome annotation indicated the existence of three candidate genes in this region that may be related to ratooning ability. Through gene prediction and cDNA sequencing, we speculated that the target gene of ratooning ability is LOC_Os02g51930 which encodes cytokinin glucosyl transferases (CGTs), hereafter named qRA2. Further analysis showed that qra2 was a 1-bp substitution in the first exon in NIL128, which resulted in the premature termination of qRA2. The results of the knockdown experiment showed that the Jiafuzhan knockdown mutants exhibited the ratooning ability phenotype of NIL128. Interestingly, the qRA2 gene was found to improve ratooning ability without affecting major agronomic traits. These results will help us better understand the genetic basis of rice ratooning ability and provide a valuable gene resource for breeding strong ratoon rice varieties.

Early harvesting and increasing stubble-cutting height enhance ratoon rice yield

Summary To clarify the combined effects of the cutting time and cutting height on ratooning ability and rice grain yield of the ratoon crop in the novel ratoon rice cropping, a field experiment was carried out to investigate the combined effects of harvesting time and the stubble-cutting height of the main crop on the growth duration, ratooning ability and grain yield of the ratoon crop. The growth period was shortened by 3.5 days on average when the harvesting time was 10 days ahead of time. On average, the growth duration was prolonged by 7 days per each decrease of 10 cm stubble height. Early harvesting and increasing stubble-cutting height greatly increased the grain yield of the ratoon crop. The highest grain yield was achieved at 10 days after flowering stage and a stubble height of 30 cm, which were 6916 kg·hm−2 for XLY900 and 7262 kg·hm−2 for YY4149, averaged across years. High rice yield of the ratoon crop was mainly depended on panicle numbers and grain-filling percentage, rather than spikelets per panicle. Increasing cutting height and the cutting time of the main crop ahead maintain more stubble biomass and nitrogen content. A significant positive correlation was observed between stubble nitrogen content and tillers-to-stubble ratio (TSR), as well as a significant positive relation was found between panicle-to-stubble ratio and TSR. Therefore, cutting 10 days after flowering stage of the main crop with 30 cm stubble-cutting height enhances ratooning ability due to higher stubble biomass and nitrogen content, and then increases rice yield of the ratoon crop.