Extreme temperatures are considered one of the main constraints that limit the growth and development of rice. We elucidated the root and shoot developmental plasticity of 64 rice genotypes during early seedling establishment, using the sunlit plant growth chambers at 22/14 (low), 30/22 (optimum), and 38/30 °C (high) day/night temperatures. Low temperature severely inhibited 23 traits, such as shoot (68%), root (57%), and physiological (35%) attributes. On the contrary, the high temperature positively affected most of the shoot (48%) and root (31%) traits, except root diameter and root/shoot ratio, compared with the optimum. Alternatively, leaf chlorophyll fluorescence-associated parameters declined under low (34%) and high (8%) temperatures. A weak correlation between cumulative high-temperature response index (CHTRI) and cumulative low-temperature response index (CLTRI) indicates the operation of different low- and high-temperature tolerance mechanisms at the early seedling stage. Groups of distinct rice genotypes associated with low or high-temperature tolerance were selected based on CHTRI and CLTRI. The genotypes that commonly performed well under low and high temperatures (IR65600-81-5-2-3, CT18593-1-7-2-2-5, RU1504114, RU1504122, Bowman, and INIA Tacuari) will be valuable genetic resources for breeders in developing early-season high- and low-temperature-tolerant genotypes for a broad range of both tropical and temperate rice-growing environments.

Drought is a major abiotic stress factor affecting the growth and development of plants at all stages. Developing a screening tool for identifying drought stress tolerance during seedling establishment is important in the deployment of rice varieties suited to water-limited growing environments. An experiment was conducted to evaluate 100 rice genotypes, mostly belonging to the tropical japonica subspecies, for drought stress tolerance using low-cost, pre-fabricated mini-hoop structures. The rice seedlings were subjected to two different soil moisture regimes- control pots managed at 100% and drought pots at 50% field capacity, from 12 to 30 days after sowing (DAS). Several morpho-physiological parameters including root traits were measured to assess the response of genotypes to drought stress. Significant moisture stress × genotype interactions were found for most of the parameters measured. A cumulative drought stress response index (CDSRI) was developed by adding the individual response indices of all cultivars. Based on CDSRI and standard deviation values, 5 and 28 genotypes were identified as highly sensitive and sensitive to drought, respectively, and 45 as moderately sensitive. On the other hand, 16 and 6 genotypes were classified as tolerant and highly tolerant to drought, respectively. Cheniere, a released cultivar, and RU1402174, an experimental breeding line, were identified as the least and most tolerant to drought among the 100 genotypes tested. Significant linear correlation coefficients were obtained between CDSRI and root growth parameters (R² = 0.91, n = 100) and CDSRI with shoot growth parameters (R² = 0.48, n = 100), revealing the importance of root traits in studying and identifying drought tolerant lines during the seedling establishment stages in rice. The tolerant rice genotypes identified will be valuable for rice scientists in studying the mechanism for early season drought as well as for rice breeders for developing new genotypes best suited under growing environments prone to early-season drought.

Rice (Oryza sativa L.) is an essential staple food crop, but the per acre average rice yield is less than its substantial potential in many countries. Rice breeders and growers would benefit from a robust genotypes with better morpho-physiological and yield-related traits. Here, seventy-four new rice genotypes were phenotyped over two years for their gas exchange and yield potential-related traits under Mississippi rice-growing conditions. A wide range of variability was observed among genotypes for all measured traits. Detailed phenotyping of rice genotypes revealed two key relationships that function together to contribute to yield potential under the southern US climate. The first one, grain yield, grain number, and spikelet fertility, showed considerable correlation (r = 0.45 to 0.79, p < 0.001) to harvest index. Conversely, days to anthesis had a high and negative correlation with harvest index (r = −0.79, p < 0.001), which suggests that selection for short duration genotypes with efficient partitioning could improve the yields under southern US climatic conditions. Additive response index revealed a higher positive association with yield traits (R² = 0.59) than physiological (R² = 0.28) and morphological traits (R² = 0.21). Compared with the commercial genotype Rex, 21.6% and 47.3% of the rice genotypes had a higher gas exchange and yield response scores. IR08A172, IR07K142 and IR07F287 were ranked as high performers in physiological and yield response indices. Our study highlights that selection for short-duration yield-related traits with efficient sink capacity traits is desirable for future breeding programs.

Drought stress is one of the most devastating abiotic factors limiting plant growth and development. Devising an efficient and rapid screening method at the seedling stage is vital in identifying genotypes best suited under drought conditions. An experiment was conducted to assess 74 rice genotypes for drought tolerance using specially designed mini-hoop structures. Two treatments were imposed on rice seedlings, including 100% moisture and a 50% moisture regime. Several shoot morpho-physiological traits and root traits were measured and analyzed. The genotypes exhibited a wide range of variability for the measured traits, with the leaf area showing the most significant variation, followed by plant height, tiller number, and shoot dry weight. In contrast, the drought did not significantly affect most root traits. The germplasm was classified into different categories using cumulative drought stress response indices (CDSRI); 19 genotypes (26%) were identified as drought sensitive, and 33 (45%), 15 (20%), and 7 (9%) were determined as low, moderately, and highly drought-tolerant, respectively. Genotypes IR86638 and IR49830 were the most and least drought-tolerant, respectively. Overall, a poor correlation was observed between CDSRI, total shoot traits (R² = 0.36), and physiological parameters (R² = 0.10). A strong linear correlation was found between CDSRI and root traits (R² = 0.81), suggesting that root traits are more crucial and better descriptors in screening for drought tolerance. This study can help rice breeders and scientists to accelerate breeding by adopting a mini-hoop rapid screening method. The tolerant genotypes could serve as appropriate donor parents, progenies, and potential genotypes for developing drought-tolerant commercial cultivars.

تعد معدلات البذور عاملاً مهمًا يؤثر على الصفات الخضرية، التكاثرية والحاصل للحنطة Triticum aestivum L لذلك، تمت دراسة استجابة الأصناف لمعدلات البذور المختلفة لإيجاد توليفة مناسبة فيما بينها. تم إجراء التجربة بثلاثة مكررات باستخدام تصميم القطع المنشقة ضمن تصميم القطاعات العشوائية الكاملة RCBD تم وضع ثلاث معدلات كميات بذار في قطع الألواح الرئيسية (150 ، 200 ، 250 كجم / هكتار) ، وتم وضع سبعة أصناف من القمح في قطع الألواح الثانوية (شام 6 ، تموز 2 ، لطيفة ، سالي ، اباء 99 ، ربيع ، أبو غريب). أشارت النتائج إلى أن اباء 99 خلال متوسط معدلات كميات البذار الثلاث أعطيت أعلى مساحة من ورقة العلم (44.25 سم2)، عدد الحبوب في السنبلة (78.85)، وعدد السنابل في وحدة المساحة (441.81) \م2، وحاصل الحبوب (5.9) طن \هكتار. بينما أعطى الصنف شام 6 أعلى طول للسنبلة (11.11 سم) ووزن 1000 حبة (35.20 جم). تفوقت كمية البذار الأولى (150 كجم / هكتار) خلال متوسط الأصناف السبعة على معدلات البذور الأخرى لجميع الصفات باستثناء ارتفاع النبات. أعطت التوليفة بين اباء99 وكمية البذار الأولى أعلى محصول حبوب (6.7) طن / هكتار. ومن ثم يقترح زراعة الصنف اباء99 مع كميات البذار الأول (150) كجم / ساعة في هذه المنطقة والمناطق المجاورة لها ذات الطابع البيئي المماثل....

Wheat (Triticum aestivum L) is one of the major staple food crops consumed globally. Nonetheless, the cultivation of wheat is influenced by various environmental factors, with the planting date being significantly impacted by the effects of climate change. Addressing these changes could involve evaluating wheat genotypes to identify appropriate planting dates. A phenotypic screening experiment was conducted in the field crop station of Agriculture College of Tikrit University to determine the suitable planting time for wheat cultivars under local environmental conditions during 2022-23. Several morpho-physiological, quality, and yield traits were measured. Factorial experiment using spilt plot through randomized completely block design (RCBD). was used with three replications. The five planting dates (5-10, 25-10, 15-11, 5-12, and 25-12) were considered as the main plot, and the eight wheat cultivars (Ipaa99, Al-Rasheed, Al-Baraka, Sham6, Tammuz2, Al-Hashimiya, Al-Noor, and Al-Adnanieh) as sub-main plot. Data were used to calculate the Individual, Cumulative, and Total Vigor Response Indices (IRI, CRI & TRI). Cultivars were classified into different categories using total cumulative early or late planting date vigor response index values (TRI-e) or (TRI-l) and standard deviation (SD). The (TRI-e) values ranged from 36.07 (sensitive) for the cultivar Al-Baraka to 39.13 (tolerant) for the cultivar Al-Hashimiya. However, the (TRI-l) values ranged from 36.59 (sensitive) for the cultivar Al-Noor to 39.52 (tolerant) for the cultivar Al-Hashimiya. The correlation coefficient (r2) between the (TRI-e) and cumulative very early/early planting date vigor response index was positively correlated (r2 = 0.70 for very early planting date (5-Oct) and r2 = 0.60 for early planting date (25-Oct). Furthermore, 76% of the total variation in the (TRI-l) was explained by the cumulative very late planting date vigor response index (CRI-vl) while just 49% of the total variation was explained by the cumulative late planting date vigor response index (CRI-l). Based on those results, wheat producers could select either tolerant cultivars for early planting or tolerant cultivars for late planting to maximize wheat production in their specific growing environments including planting dates.