Inbred Cultivars Research Articles

Analytical prediction of genetic contribution across multiple recurrent backcrossing generations.

We derive formulas for the residual donor genome content during trait introgression via recurrent backcrossing and use these formulas to predict (without simulation) residual donor genome content for five future generations. Trait introgression is a common method for introducing valuable genes or alleles into breeding populations and inbred cultivars. The particular breeding scheme is usually designed to maximize the genetic similarity of the converted lines to the recurrent parent while minimizing cost and time to recover the near isogenic lines. Key variables include the number of generations and crosses and how to apply genotyping and selection. One form of trait introgression, which is our focus, involves an initial cross of an elite, homozygous recurrent parent line with a non-recurrent, homozygous donor line. The descendants of this cross are backcrossed with the recurrent parent for several generation before self-pollination in the final generation to recover lines with the alleles of interest. In this paper, we derive analytical formulas that characterize the stochastic nature of residual donor genome content during this form of trait introgression. The development of these formulas expands the mathematical methods one can integrate into breeding design. In particular, we show we can use our formulas in a novel mathematical program to allocate resources to optimize the reduction of residual donor genome content.

Ecological implications of row width and cultivar selection on rice (Oryza sativa) and barnyardgrass (Echinochloa crus-galli)

Rice (Oryza sativa L.) producers in the Mid-south are experiencing difficulties with herbicide-resistant weeds such as barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.]. As a result, methods that can alter E. crus-galli ecology are needed. This research evaluated the ecological implications of rice cultivar and row widths on crop and E. crus-galli growth. Overall, for E. crus-galli, as the row width increased, greater density, panicle counts, and seed production occurred. Echinochloa crus-galli density was 120% greater in a 38-cm row width than the 13-cm row width at the preflood rice stage. Reduced early-season rice canopy coverage in the wider row widths allowed for increased E. crus-galli densities. At the preharvest stage, E. crus-galli panicle counts were similar for the 13- and 19-cm rows. Row width did not affect rice yield, indicating wider row widths could be feasible agronomically, but additional weed management efforts would be needed because greater ecological advantages were obtained in narrower rows. Less E. crus-galli seed production occurred in competition with hybrid cultivars compared to inbred cultivars. Overall, the standard row width (19-cm) and hybrid cultivars would provide the greatest ecological advantage over E. crus-galli.

Optimal nitrogen management for high yield and N use efficiency of ratoon sorghum

Sorghum ratooning, a time and labor-saving cultivation practice, is increasingly being adopted by farmers in Southwest China as an alternative. Efficient N fertilizer management is critical for economical production of sorghum and the long-term protection of the environment. To investigate the impact of N management on grain yield and nitrogen use efficiencies (NUEs) of ratoon sorghum system, a three-year field experiment was conducted for Jinyunuo3 (a hybrid cultivar) and Guojiaohong1 (an inbred cultivar) using 12 combinations of N rates and splitting ratios. The results showed that increasing N rate and splitting application times led to improvements in various growth parameters such as dry matter weight, crop growth rate (CGR), leaf area index (LAI), and photosynthetic potential (PP). The main, ratoon, and annual yields increased with N rate increase, but there was no significant difference between 225 and 150 kg N ha−1 in the ratoon and annual yields. Splitting the application of N fertilizer enhanced grain yield compared to a single dose application method, especially three-split applications yielded higher than two-split applications. Compared with N rates of 225 and 150 kg ha−1, N rate of 75 kg ha−1 increased apparent recovery rate of applied nitrogen (REN), agronomic efficiency of applied nitrogen (AEN), and partial factor productivity from applied nitrogen (PFPN) in both main season and whole year. But through splitting application methods at high N rates could achieve similar or even higher levels of NUEs compared to all applied as basal fertilizer at low N rates. Therefore, it could be recommended that applying 150 kg N ha−1 with a basal-jointing-heading fertilizer ratio of 2:4:4 represented an efficient N management practice to synchronously obtain high grain yield and NUEs in ratoon sorghum system in Southwest China.

Evaluation of pollination traits important for hybrid wheat development in Great Plains germplasm

AbstractHybrid wheat (Triticum aestivum L.) offers potential yield advantages over conventional inbred cultivars. For hybrid wheat to be a commercial success, the cost to produce the hybrid seed needs to be minimized. Although wheat is naturally self‐pollinated, hybrid wheat seed production can be improved by increasing the amount and availability of pollen for cross‐pollination. This research examined 19 pollination traits using the Hard Winter Wheat Association Mapping Panel for 3 years. Anther extrusion, pollen 50 date (date at which a genotype has 50% of spikes pollinating), plant height, and pollination duration (last spike pollen 50 date minus first spike pollen 50 date) were identified as the most important traits for hybrid seed production. Anther extrusion, plant height, and pollen 50 date varied widely among genotypes, while pollination duration had significant genotypic differences in one year of testing. These traits also had significant genotype × year interactions, but better and poorer performers were consistent among years. Anther extrusion was weakly, negatively correlated with plant height, and high anther extrusion semi‐dwarf genotypes were identified. Pollination duration was reduced in a high temperature (>30°C) environment, and genotypic differences in pollination duration were identified only in a milder temperature (24°C) environment. Hierarchical clustering suggested that excellent pollinator genotypes with high anther extrusion and longer pollination duration tended to pollinate early and were of short to moderate stature. Pollination traits were higher when temperatures were mild, which benefited early genotypes because they pollinated before higher temperatures limited their pollination duration.

Whole-genome sequence of synthetically derived Brassica napus inbred cultivar Da-Ae.

Brassica napus, a globally important oilseed crop, is an allotetraploid hybrid species with two subgenomes originating from Brassica rapa and Brassica oleracea. The presence of two highly similar subgenomes has made the assembly of a complete draft genome challenging and has also resulted in natural homoeologous exchanges between the genomes, resulting in variations in gene copy number, which further complicates assigning sequences to correct chromosomes. Despite these challenges, high-quality draft genomes of this species have been released. Using third generation sequencing and assembly technologies, we generated a new genome assembly for the synthetic B. napus cultivar Da-Ae. Through the use of long reads, linked-reads, and Hi-C proximity data, we assembled a new draft genome that provides a high-quality reference genome of a synthetic B. napus. In addition, we identified potential hotspots of homoeologous exchange between subgenomes within Da-Ae, based on their presence in other independently derived lines. The occurrence of these hotspots may provide insight into the genetic rearrangements required for B. napus to be viable following the hybridization of B. rapa and B. oleracea.

Bin mapping of water stress tolerance‐related, fruit quality, and horticultural traits in tomato introgression lines derived from wild Solanum habrochaites

AbstractClimate change is reducing water availability for crop production. Cultivated tomato, Solanum lycopersicum, has a limited genetic base for improvement. A wild tomato, Solanum habrochaites, is water stress tolerant and may serve as a genetic source of abiotic stress‐tolerance traits. A set of 24 introgression lines (ILs) derived from S. habrochaites and processing tomato inbred cultivar E6203 were evaluated in the field in replicated experiments over 3 years for 15 traits, including water stress tolerance‐related, fruit quality, and horticultural traits. A split plot experimental design was employed with reduced and full irrigation treatments as main plots. Subplots consisted of the ILs and control E6203, and trait data were collected on a per‐subplot basis. Statistical data analyses and bin mapping were performed on a per‐trait basis. Trait‐genomic region associations (TGRAs) were detected in ILs when a significant difference between E6203 and an IL was present. A total of 268 TGRAs were detected for all 15 traits. Traits mapped to introgressions in 22 of the 24 ILs and in 11 of 12 tomato chromosomes. ILs contributed both positive and negative allelic effects at TGRAs. TGRA with positive allelic effects from S. habrochaites were identified for soluble solids content, fruit weight, degree of fruit sunburn, canopy cover, and maturity. Our results suggest that S. habrochaites may be a useful resource for breeding improvement of certain fruit quality and horticultural traits in cultivated tomato. Overall, S. habrochaites alleles did not contribute to increased water stress tolerance relative to E6203 at the milder level of water stress used in this study.

Genomic insight into genetic changes and shaping of major inbred rice cultivars in China.

The annual planting area of major inbred rice (Oryza sativa) cultivars reach more than half of the total annual planting area of inbred rice cultivars in China. However, how the major inbred rice cultivars changed during decades of genetic improvement and why they can be prevalently cultivated in China remains unclear. Here, we investigated the underlying genetic changes of major inbred cultivars and the contributions of landraces and introduced cultivars during the improvement by resequencing a collection of 439 rice accessions including major inbred cultivars, landraces, and introduced cultivars. The results showed that landraces were the main genetic contribution sources of major inbred Xian (Indica) cultivars, while introduced cultivars were that of major inbred Geng (Japonica) cultivars. Selection scans and haplotype frequency analysis shed light on the reflections of some well-known genes in rice improvement, and breeders had different preferences for the Xian's and Geng's breeding. Six candidate regions associated with agronomic traits were identified by genome-wide association mapping, five of which were under positive selection in rice improvement. Our study provides a comprehensive insight into the development of major inbred rice cultivars and lays the foundation for genomics-based breeding in rice.

Research progress and reflection of two-line hybrid wheat based on thermo-photo sensitive genic male sterility in Yunnan

<p indent="0mm">Wheat is one of the most important food crops in Yunnan Province. Drought and yellow rust are the main limiting factors to wheat productivity. Utilization of heterosis is expected to be a promising way to increase resistance to stress and yield potential. In 1992, photo-thermo sensitive genic male sterile wheat “ES” and thermo-photo sensitive genic male sterile wheat “C49S” were developed by Hunan Agricultural University and Chongqing Academy of Agricultural Science, respectively, which provided a new way for heterosis utilization in China by conducting two-line hybrid wheat breeding. ES and C49S were sterile under low-temperature and short-day conditions, and fertile under high-temperature and long-day conditions. During 1993–2000, ten sterile lines of ES and C49S were introduced into Yunnan for sterility identification, while only C49S-87 from Chongqing showed stable sterility in three special locations of Yunnan when sowed in middle October, with 15–20 d of sterile heading duration (bagged seed-set rate &lt;1%). In 2002, hybrid cultivar Yunza 3 from C49S-87 was released in Yunnan and increased yield by 11.4% over the inbred CK in regional tests, but was planted only 12400 ha in Yunnan due to the loss of resistance to yellow rust after 2004. Given that C49S-87 was poor in out-crossing ability (40%–50%) and susceptible to yellow rust, an improved sterile line K78S was developed from C49S-87 in 2001. K78S had 26–44 d of sterile heading duration in all regions with altitudes from <sc>1530</sc> to <sc>2400 m</sc> when sowed from middle October to early November, as well as better out-crossing ability (70%–80%) and higher resistance to yellow rust. In 2004 and 2005, Yunza 5 and Yunza 6 developed from K78S were separately released in Yunnan. Both cultivars showed higher yield increase by &gt;15% in regional tests. Meanwhile, high cross-pollination ability of K78S markedly raised the yield of hybrid seed production from 1500–1800 kg/ha of Yunza 3 to 3900–4500 kg/ha of Yunza 5 and Yunza 6 when the same techniques of mechanized seed production were applied. These cultivars have been totally planted about 700000 ha in Yunnan and parts of Vietnam till now. However, since 2005, no hybrid cultivar has been released in Yunnan. The main reasons are as follows: (1) Only two sterile lines were practically used for test-crossing before 2020 but became susceptible to yellow rust ten years ago, which greatly reduced the opportunities of creating high heterotic hybrids although thousands of restorers were test-crossed. In 2020, 24 elite sterile lines were developed by using doubled haploid (DH) breeding, and have been used in hybrid wheat breeding now. (2) Most restorers were “by-products” of developing inbred cultivars, thus the combining ability between the sterile line and the restorer was never tested during the developing of restorers, resulting in completely random or accidental emergence of heterotic hybrids. Therefore, it might be necessary to re-construct the restorer breeding program by using dwarf-male-sterile wheat with reference to maize inbred line breeding. In addition, exploitation of nucleo-cytoplasmic heterosis might be another way to increase heterosis both in yield potential and resistance to stress, as suggested by Kihara in 1979. Generally, some promising progress in two-line hybrid wheat breeding based on thermo-photo sensitive genic male sterility has been achieved in Yunnan during past <sc>30 years.</sc> However, more efforts should be made in breeding and basic research to efficiently create hybrids with higher yield increase and better resistance to drought and diseases, and this will improve the current system and promote the wider application of hybrid wheat in Yunnan.

Impact of breeder seed multiplication and certified quality seed distribution on rice production in India

BackgroundThe All India Coordinated Rice Improvement Project (AICRIP) organizes multi-location tests (METs) with new genotypes from breeding programs. The best performing genotypes in METs for 3–4 years are identified and notified as commercial cultivars by the Government of India (GOI) to authorize breeder seed (BS) production.MethodsWe created a database and analyzed data on BS production for 24 years (1995–96 to 2018–19) in 475 inbred and 22 F1 hybrid cultivars. Estimates were made to rank cultivars on the proportional contribution of a cultivar, quantity produced and a new BS index. Correlation and regression analyses were used to find the relationships between BS, certified quality seed distributed (CQSD), and milled rice production. We compared cultivars in BS production chain with those grown in farmers’ fields across the country as identified in the production-oriented surveys.ResultsThe top ten inbred cultivars identified are Jaya (notified by GOI in 1969), Swarna, Kranthi, IR 36, Sarjoo 52, Samba Mahsuri and Pusa Basmati 1 (notified in 1980–1989), and IR 64, Vijetha and Cottondora Sannalu (notified in 1991–2000). BS production in hybrid F1 was insignificant. We detected a Pearson correlation (r = 0.806, P < 0.01) between the BS production and CQSD, and a linear relationship between the annual rice production in India and the CQSD (R2 = 0.850, P < 0.01). The rice area coverage in 2018–19 with CQSD estimated was 41%. A total of 1877 cultivars (528 notified and 1349 not notified) were found at farms in rice growing districts in India.ConclusionsFrom 1995–2019, BS and CQSD together increased the annual milled rice production in step with increases in population. Diverse rice genotypes have enabled rice to endure crop constraints in fragmented landholdings spread over 43 m ha. AICRIP’s efforts have sustained availability of > 73 kg rice per capita per year (~ 40% of food grains). The process of notification, receipt of indent for BS from states, allotment and BS production, and de-notification of a cultivar by GOI need a review to ensure profits to farmers. As the 1000-seed weight varies in cultivars, it must be notified by GOI to adjust seed rate and maintain the recommended plant population at the farms. There is scope to increase the priceless BS production in cultivars to raise the country’s production further, facilitate export and ensure profits to all stakeholders.

Grain yield performance of hybrid rice in relation to inbred cultivars in long‐term multi‐environment tests in India

AbstractWe analyzed the yield data of 2,070 rice hybrid F1 genotypes with inbred local cultivars (ILCv) evaluated over 32 yr (from 1988 to 2019) in 2,376 multi‐environment experiments executed at 102 locations in the irrigated ecosystem across India. The genetic gain or loss in yield of hybrid F1 genotypes estimated over the test duration was nonsignificant. The differences were highly significant between the means of group of F1 hybrid genotypes with yields higher than ILCvs in 985 experiments and the group of F1 hybrid genotypes with yields lower than ILCvs in 962 experiments. Hybrids produced 10% more yield (728–2,588 kg ha–1) than ILCvs in 672 experiments at several locations. Our analyses have established that grain yields of 7.0–7.9 Mg ha–1, were harvested in hybrid F1 genotypes with early‐ (110–120 d), mid‐early‐ (121–130 d), and medium‐ (131–140 d) maturity duration, and in those with medium slender grains (130±5 d) at many locations in 374 out of the 985 experiments. A higher level of rice (Oryza sativa L.) productivity per day (62–63 kg ha–1) was recorded with the early‐maturing and mid‐early‐maturing hybrid genotypes. Both the hybrid F1 genotypes and ILCvs produced grain yields (≥10 Mg ha–1) similar to values that were recorded previously with commercial inbred cultivars since 1968 at many locations. The attainable grain yield records of ILCvs were not broken by the yields of hybrid F1 genotypes. Hence the doubt arises whether there was any overestimation of hybrid genotypes or an underestimation of inbred yields. Therefore, any genetic gain or loss for grain yields in new genotypes developed in experiments can be estimated only when ILCvs produce their attainable yield recorded previously. There is scope for breeders to limit test locations to represent specific target areas to avoid data loss.

Hybrids Provide More Options for Fine-Tuning Flowering Time Responses of Winter Barley.

Crop adaptation requires matching resource availability to plant development. Tight coordination of the plant cycle with prevailing environmental conditions is crucial to maximizing yield. It is expected that winters in temperate areas will become warmer, so the vernalization requirements of current cultivars can be desynchronized with the environment’s vernalizing potential. Therefore, current phenological ideotypes may not be optimum for future climatic conditions. Major genes conferring vernalization sensitivity and phenological responses in barley (Hordeum vulgare L.) are known, but some allelic combinations remain insufficiently evaluated. Furthermore, there is a lack of knowledge about flowering time in a hybrid context. To honor the promise of increased yield potentials, hybrid barley phenology must be studied, and the knowledge deployed in new cultivars. A set of three male and two female barley lines, as well as their six F1 hybrids, were studied in growth chambers, subjected to three vernalization treatments: complete (8 weeks), moderate (4 weeks), and low (2 weeks). Development was recorded up to flowering, and expression of major genes was assayed at key stages. We observed a gradation in responses to vernalization, mostly additive, concentrated in the phase until the initiation of stem elongation, and proportional to the allele constitution and dosage present in VRN-H1. These responses were further modulated by the presence of PPD-H2. The duration of the late reproductive phase presented more dominance toward earliness and was affected by the rich variety of alleles at VRN-H3. Our results provide further opportunities for fine-tuning total and phasal growth duration in hybrid barley, beyond what is currently feasible in inbred cultivars.

Effects of increasing panicle-stage N on yield and N use efficiency of indica rice and its relationship with soil fertility

Because of the higher nitrogen (N) recovery efficiency (NRE) of panicle-stage fertilization compared with basal and tillering fertilization, increasing the proportion of N topdressing at the booting stage (panicle-N) is recommended and commonly practiced in parts of China. To investigate the effects of increasing panicle-N on grain yield and N use efficiency (NUE) and the relationships of the increase and the rice cultivar and soil fertility status, we increased the percentage of panicle-N from 20% to 40% by correspondingly reducing the N amount applied only at the tillering stage in both high- and low-fertility blue clayey paddy fields in 2018 and 2019. Four indica cultivars with diverse panicle types were used, and their grain yield, dry matter accumulation, and NUE were compared. In high-fertility soil, increasing topdressing panicle-N from 20% to 40% reduced tillering ability and reduced the effective panicle numbers of the multi- and medium-panicle cultivars Huanghuazhan (HHZ), C Liangyouhuazhan (CHZ), and Tianyouhuazhan (THZ). These cultivars gave the greatest yield when 30% of N was supplied as panicle fertilizer, whereas the yield, NRE, N agronomic efficiency (NAE), and nitrogen physiological efficiency (NPE) of the heavy-panicle inbred cultivar Yangdao 6 (YD6) continued to increase, resulting in improved dry matter accumulation and grain filling in the late growth stage. The yield, NAE, NRE, and NPE of YD6 peaked when the panicle-N constituted 40%. While in low-fertility soil, the multipanicle cultivar HHZ showed the greatest yield when 30% of fertilizer-N was applied once at the panicle initiation (PI) stage, while the medium-panicle cultivar CHZ showed the greatest yield when the panicle-N percentage was 40%. Our results suggest that the percentage of panicle-N fertilizer should not exceed 30% for multipanicle cultivars, while can be appropriately increased to 40% for heavy-panicle indica cultivars. The effect of increasing topdressing panicle-N on the yield of medium-panicle cultivars was related to soil fertility. The optimum panicle-N percentage was 30% in the high-fertility soil and 40% in the low-fertility soil.

Application of K and Zn Influences the Mineral Accumulation More in Hybrid Than Inbred Maize Cultivars.

Maize (Zea mays L.) is an important crop used for feeding humans and cattle globally. Deficiency of potassium (K) and zinc (Zn) adversely impacts the maize crop productivity and quality. However, the application of these nutrients shows variant responses in different maize cultivars. To understand this perspective, the current study aimed at investigating K and Zn’s optimal concentration in different hybrid and inbred maize cultivars. The treatments were based on three zinc levels (0, 6, and 12 mg Zn kg−1) and K levels (0, 30, and 60 mg kg−1), and their respective combinations. The experiment results showed that combined fertilization approaches of Zn and K (Zn12K60) improved the plant biometric, and physiological attributes of maize crop. The results revealed a significant increase in plant height (45%), fresh weight (70%), and dry weight (45%). Similarly, physiological attributes significantly improved the relative water content (76.4%), membrane stability index (77.9%), chlorophyll contents (170%), and photosynthetic rate (130%) in both inbred and hybrid genotypes. Furthermore, Zn and K (Zn12K60) increased transpiration rate (E), stomatal conductance (Ci), and internal CO2. In conclusion, maize hybrids (Neelam and DK-6142) were observed best compared with inbred (Afghoi and P-1543) cultivars with the combined application of Zn and K (Zn12K60). Thus, these inbred varieties should be preferred for fodder requirement with optimum fertilizer (Zn12K60) application in Zn deficient soils.

Impact of tillage and crop establishment methods on rice yields in a rice-ratoon rice cropping system in Southwest China

Simplified cultivation methods for rice production offer considerable social, economic, and environmental benefits. However, limited information is available on yield components of rice grown using simplified cultivation methods in a rice-ratoon rice cropping system. A field experiment using two hybrid and two inbred rice cultivars was conducted to compare four cultivation methods (conventional tillage and transplanting, CTTP; conventional tillage and direct seeding, CTDS; no-tillage and transplanting, NTTP; no-tillage and direct seeding, NTDS) in a rice-ratoon rice system from 2017 to 2020. Main season yields for CTDS and NTDS were higher than for CTTP by 6.1% and 2.8%, respectively; whereas ratoon season yields for CTDS and NTDS were equal to or higher than for CTTP. Annual grain yields for CTDS and NTDS were higher than for CTTP by 4.4% and 3.2%, respectively. The higher CTDS and NTDS yields were associated with higher panicle numbers per m2 and biomass production. Rice hybrids had higher yields than inbred cultivars by 15.8–19.3% for main season and by 15.6–19.4% for ratoon season, which was attributed to long growth duration, high grain weight and biomass production. Our results suggest that CTTP can be replaced by CTDS and NTDS to maintain high grain yields and save labor costs. Developing cultivars with high grain weight could be a feasible approach to achieve high rice yields in the rice-ratoon rice cropping system in southwest China.

Seeding Rate Effects on Hybrid Spring Wheat Yield, Yield Components, and Quality

Agronomic practices, such as planting date, seeding rate, and genotype, commonly influence hard red spring wheat (HRSW, Triticum aestivum L. emend. Thell.) production. Determining the agronomic optimum seeding rate (AOSR) of newly developed hybrids is needed as they respond to seeding rates differently from inbred cultivars. The objectives of this research were to determine the AOSR of new HRSW hybrids, how seeding rate alters their various yield components, and whether hybrids offer increased end-use quality, compared to conventional cultivars. The performance of two cultivars (inbreds) and five hybrids was evaluated in nine North Dakota environments at five seeding rates in 2019−2020. Responses to seeding rate for yield and protein yield differed among the genotypes. The AOSR ranged from 3.60 to 5.19 million seeds ha−1 and 2.22 to 3.89 million seeds ha−1 for yield and protein yield, respectively. The average AOSR for yield for the hybrids was similar to that of conventional cultivars. However, the maximum protein yield of the hybrids was achieved at 0.50 million seeds ha−1 less than that of the cultivars tested. The yield component that explained the greatest proportion of differences in yield as seeding rates varied was kernels spike−1 (r = 0.17 to 0.43). The end-use quality of the hybrids tested was not superior to that of the conventional cultivars, indicating that yield will likely be the determinant of the economic feasibility of any future released hybrids.

Night Temperature Determines the Interannual Yield Variation in Hybrid and Inbred Rice Widely Used in Central China Through Different Effects on Reproductive Growth.

Interannual variation in grain yield of rice has been observed at both farm and regional scales, which is related to the climate variability. Previous studies focus on predicting the trend of climate change in the future and its potential effects on rice production using climate models; however, field studies are lacking to examine the climatic causes underlying the interannual yield variability for different rice cultivars. Here a 6-year field experiment from 2012 to 2017 was conducted using one hybrid (Yangliangyou6, YLY6) cultivar and one inbred (Huanghuazhan, HHZ) cultivar to determine the climate factors responsible for the interannual yield variation. A significant variation in grain yield was observed for both the inbred and hybrid cultivars across six planting years, and the coefficient of variation for grain yield was 7.3–10.5%. The night temperature (average daily minimum temperature, Tmin) contributed to the yield variability in both cultivars. However, the two cultivars showed different responses to the change in Tmin. The yield variation in HHZ was mainly explained by the effects of Tmin on grain filling percentage and grain weight, while the change in spikelets m−2 in response to Tmin accounted for the yield variability in YLY6. Further analysis found that spikelets m−2 of YLY6 significantly and negatively correlated with Tmin from transplanting to heading. For HHZ, the grain filling percentage and grain weight were significantly affected by Tmin of the week prior to heading and from heading to maturity, respectively. Overall, there were differences in the response mechanism between hybrid and inbred cultivars to high night temperature. These will facilitate the development of climate-resilient cultivars and appropriate management practices to achieve a stable grain yield.

Assessment of tolerance and resistance of inbred rice cultivars to combined infestations of rice water weevil and stemborers

AbstractPlants possess defense‐related traits that both reduce injury from herbivores (resistance) and the amount of yield loss per unit injury (tolerance). Plant resistance and tolerance can be utilized in pest management programs. The rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), is the most destructive early‐season pest of rice (Oryza sativa L., Poaceae) in the USA. Additionally, lepidopteran stemborers, particularly the invasive Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), are increasing in economic importance as pests of rice in Louisiana, USA. This study was conducted to evaluate both the resistance and tolerance of commonly grown inbred rice cultivars in Louisiana to combined infestations of rice water weevils and stemborers. Field experiments were established at the Rice Research Station in Crowley, LA, USA from 2017 to 2019. Eight commonly grown inbred cultivars were selected and pest infestation levels were manipulated using insecticidal seed treatments. The rice cultivar ‘Jupiter’ supported the highest numbers of immature rice water weevils, whereas weevil densities on other cultivars were intermediate. Low levels of stemborer injury were observed in ‘Cheniere’ and ‘Jazzman‐2’, which suggests that these cultivars express some resistance to stemborers, whereas high stemborer injury was observed in ‘Cocodrie, ‘CL151’, and ‘Mermentau’. Together, rice water weevil and stemborer infestations negatively affected rice yields, with losses up to 18%. However, differences among cultivars in overall yield losses were minimal. Comparisons of slopes of yield × weevil density relationships among cultivars revealed a greater decline, that is, yield loss per weevil, for Cheniere relative to Cocodrie. Our data suggest that plant resistance can serve as a valuable component of an integrated pest management program, particularly for stemborers.

Agronomic performance of improved pearl millet cultivars in southern Chad

Pearl millet [Pennisetum glaucum (L.) R. Br.] is a vital staple food crop for poor people in dry-land areas. It plays an important role on human consumption in South of Chad where farmers always used landraces with a little adoption of improved cultivars. Evaluation of agronomic performance of inbred cultivars at research station is important to identify the high performance genotype to be released as new cultivars in farmer area. So, five improved varieties associated with a well-known variety from research were evaluated for ten agronomical traits. Experiment was carried out during rainy season of 2019 at the research station of Bébédjia, South of Chad. The results of the analysis of variance of assessed traits showed high significant differences (p&lt;0.001) for spike girth and slight significant difference (p&lt;0.05) for days to flowering, thousand seeds weight and productive tillers per plant. An important positive and significant correlations were also noted between day to flowering and number of grains per plot (r = 0.7; p&lt;0.01), seed weight per plot (0.684; p&lt;0.01) and potential grain yield (r = 0.684; p&lt;0.01). Moreover, three cultivars with an important potential grains yield namely ICMV167006 (4.99 t.ha−1), ICMV 167005 (4.68 t.ha−1) and ICMV177111 (3.98 t.ha−1) were identified. Otherwise, for the days to flowering, the cultivars ICMV167006 (73.67 days), ICMV 167005 (75.33 days) are earlier than ICMV 177 111 (78.67 days). These cultivars could be proposed to be released in farmer area as novel cultivars.

Interactive Effect of Weeding Regimes, Rice Cultivars, and Seeding Rates Influence the Rice-Weed Competition under Dry Direct-Seeded Condition

Dry direct-seeded rice (Oryza sativa L.), a climate-smart and resource-efficient (labor and water) rice production technology is gaining popularity in many parts of Asian countries; however, weeds are the major constraints for its early establishment and optimum productivity. Chemical weed management is effective, rapid, and also decreases weed management costs in dry direct-seeded rice (DSR) system; however, chemical use for weed management have a negative effect on the environment and also have human health hazards. Therefore, integrated weed management (IWM) is the best option for the sustainability of rice production under the DSR system. Improving competitiveness against weeds, weed-competitive rice cultivars, and high seeding rates were found to be the most promising IWM strategies in DSR. In this context, a field study was conducted to evaluate the weed competitiveness of rice cultivars and seeding rates on the performance of aus rice in dry direct-seeded systems in Bangladesh. Three inbred rice cultivars (CV), namely “BRRI dhan26”, “BRRI dhan48”, and “BRRI dhan55”, and one hybrid cultivar, “Arize” were tested in a seeding rate (SR) of 20, 40, and 80 kg ha−1 under two weeding regimes (WR) of weed-free and partially-weedy. Rice grain yield was strongly affected (p &lt; 0.01) by the interactions of WR, CV, and SR. In weed-free conditions, the yield of all three inbred cultivars was increased up to SR of 40 kg ha−1 and for the hybrid cultivar, up to SR of 20 kg ha−1, and with further increment of SR, there was no yield advantage. Conversely, under partially weedy conditions, the yield of three inbred cultivars increased up to SR of 80 kg ha−1; however, for the hybrid cultivar, this increment was up to SR of 40 kg ha−1 and thereafter, no yield gain. In weedy conditions, the higher SR compensates for the yield losses by increasing the competitiveness of rice with weeds. Across SR, the hybrid cultivar had a significantly (p &lt; 0.01) higher weed competitive index (WCI) than all the inbred cultivars and the highest SR always had a higher WCI.

Rice cultivar response to sublethal concentrations of glyphosate and paraquat late in the season

AbstractDifferential tolerance may be observed among rice cultivars with desiccant exposure events during rice reproduction and ripening. Five field studies were established at the Mississippi State University Delta Research and Extension Center in Stoneville, MS, to determine the effects of exposure to sublethal concentrations of common desiccants across multiple rice cultivars. Rice cultivars in the study were ‘CLXL745’, ‘XL753’, ‘CL163’, ‘Rex’, and ‘Jupiter’. Desiccant treatments included no desiccant, paraquat, or glyphosate and were applied at the 50% heading growth stage respective to cultivar. Differential injury estimates among cultivars and desiccant treatments was observed when glyphosate or paraquat was applied at 50% heading. Injury from glyphosate at 50% heading was nondetectable across all cultivars. However, injury following paraquat applications was &gt;7% across all rating intervals and cultivars. Hybrid cultivars exhibited less injury with paraquat applications than the inbred cultivars in the study. Rice following exposure to glyphosate or paraquat at 50% heading growth stage produced rough rice grain yield decreases ranging from 0% to 20% and 9% to 21%, respectively. Rough rice grain yield decreases were observed across all cultivars following paraquat exposure, and all inbred cultivars following glyphosate exposure. Across desiccant treatment, head rice yield was reduced in three of five cultivars in the study. When pooled across cultivar, paraquat applications cause a head rice yield reduction of 10%, whereas rice yield following glyphosate application remained &gt;95%. Although differential tolerance among cultivars to paraquat or glyphosate exposure was observed, impacts on grain quality coupled with yield reductions suggests extreme rice sensitivity to exposure to sublethal concentrations of these desiccants at the 50% heading growth stage.