Upland Cultivars Research Articles

Adaptability evaluation of switchgrass ( Panicum virgatum L.) cultivars on the Loess Plateau of China

In the study, the growth traits, photosynthesis and morphology characteristics of several cultivars of switchgrass ( Panicum virgatum L.) have been assessed the yield potential and adaptability in diverse environments (Yangling, Dingbian of Shaanxi province, Guyuan of Ningxia) on the Loess Plateau of China. Alamo was the best adapted switchgrass cultivar for biomass production in Yangling with dry matter (DM) yields of 44.22 t/ha; Illinois USA and Cave-in-Rock grown at Guyuan had DM yield of 10.59 t/ha and 9.36 t/ha, respectively. Similarly, Cave-in-Rock in Dingbian performed better than others except the lowland cultivars (Alamo and Kanlow), which could not overcome cold stress at Guyuan and Dingbian. Moreover, Cave-in-Rock and Nebraska 28 has the highest photosynthesis rate which reflects its high productivity. Nebraska 28 and Pathfinder shown strong drought tolerance due to their higher WUE. It appears that the upland cultivars with high ploidy (e.g. 8 n) would have better establishment than lowland varieties there. Optimal mown management seems to enhance the growth and productivity of switchgrass. Morphological characteristics were further studied using light-and scanning electron microscopy (SEM). Silica particles, vacuole size and other traits in switchgrass tissues (stem, leaf and root), as well as trichomes (leaf) showed that Cave-in-Rock and Pathfinder had larger stoma area, up to 824.4 μm 2 and 770.1 μm 2, respectively. Silica particle length was the longest in Pathfinder and shortest in Cave-in-Rock. There was a highest density of silica particles in cv. Forestberg, and lowest in Cave-in-Rock and Pathfinder. The morphological characters seemed to be associated with their ploidy levels and the arid habitat from which they were selected. Therefore, if switchgrass is to be introduced and extended on the Loess Plateau of China, Cave-in-Rock and other upland cultivars with a high chromosome ploidy might be optimal choices for biomass plants.

Assessing Genetic Diversity of Rice Varieties under Drought Stress Conditions

In order to compare different rice genotypes grown under drought stress conditions a field experiment was conducted. In this study thirty different genotypes of native, breeded and upland cultivars were evaluated. Analysis of variance showed significant differences among genotypes in respect of all vegetative and morphological traits. Genotypes were devided into three groups by cluster analysis based on all studied traits with minimum variance method (Wards Method). The total average indicates significant differences among groups in respect of all morphological and physiological characteristics. In addition, eight drought stress tolerance indices including: sensitivity to stress index (SSI), drought response index (DRI), relative drought index (RDI), tolerance index (TOL), mean productivity index (MP), stress tolerance index (STI), geometric mean productivity index (GMP) and harmonic mean index (HM) were calculated according to their grain yield under drought stress and normal conditions. In general, results of this experimnet revealed that, among rice cultivars Domsephid, Deylamany, Hasansaraei, Sadri, Anbarboo and Domsiah had the highest sensitivity referring to drought stress and produced the lowest grain yield. Also, genotypes of IR24 (breeded of IRRI), Nemat, Sephidroud, Kadoos and Bejar (breeded of Iran) and Vandana, upland cultivar (originally from India) had the highest tolerance to drought stress and produced the highest grain yield. In conclusion, it was suggested that, these cultivars are suitable for drought stress conditions and are appropriate for hybridization with the aim of increasing drought tolerance.

Clash of the Titans: Comparing Productivity Via Radiation Use Efficiency for Two Grass Giants of the Biofuel Field

The comparative productivity of switchgrass (Panicum virgatum L.) and Miscanthus (Miscanthus × giganteus) is of critical importance to the biofuel industry. The radiation use efficiency (RUE), when derived in an environment with non-limiting soil water and soil nutrients, provides one metric of relative productivity. The objective of this study was to compare giant Miscanthus to available switchgrass cultivars, using established methods to calculate RUE of the two species at two disparate sites. Measurements of fraction intercepted photosynthetically active radiation (PAR) and dry matter were taken on plots at Elsberry, MO (Miscanthus and the switchgrass cultivars Alamo, Kanlow, and Cave-in-Rock) and at Gustine, TX (Miscanthus and Alamo switchgrass, irrigated with dairy wastewater and a non-irrigated control). In MO, Miscanthus mean RUE (3.71) was less than Alamo switchgrass mean RUE (4.30). In TX under irrigation, Miscanthus mean RUE was 2.24 and Alamo switchgrass mean RUE was 3.20. In MO, the more northern lowland switchgrass cultivar, Kanlow, showed similar mean RUE (3.70) as Miscanthus. In MO, the northern upland cultivar Cave-in-Rock had a mean RUE (3.17) that was only 85% of that for Miscanthus at MO. Stress (water and nutrients) had a greater effect on Miscanthus RUE than on switchgrass RUE in TX. These results provide realistic RUE values for simulating these important biofuel grasses in diverse environmental conditions.

Dro1, a major QTL involved in deep rooting of rice under upland field conditions

Developing a deep root system is an important strategy for avoiding drought stress in rice. Using the 'basket' method, the ratio of deep rooting (RDR; the proportion of total roots that elongated through the basket bottom) was calculated to evaluate deep rooting. A new major quantitative trait locus (QTL) controlling RDR was detected on chromosome 9 by using 117 recombinant inbred lines (RILs) derived from a cross between the lowland cultivar IR64, with shallow rooting, and the upland cultivar Kinandang Patong (KP), with deep rooting. This QTL explained 66.6% of the total phenotypic variance in RDR in the RILs. A BC(2)F(3) line homozygous for the KP allele of the QTL had an RDR of 40.4%, compared with 2.6% for the homozygous IR64 allele. Fine mapping of this QTL was undertaken using eight BC(2)F(3) recombinant lines. The RDR QTL Dro1 (Deeper rooting 1) was mapped between the markers RM24393 and RM7424, which delimit a 608.4 kb interval in the reference cultivar Nipponbare. To clarify the influence of Dro1 in an upland field, the root distribution in different soil layers was quantified by means of core sampling. A line homozygous for the KP allele of Dro1 (Dro1-KP) and IR64 did not differ in root dry weight in the shallow soil layers (0-25 cm), but root dry weight of Dro1-KP in deep soil layers (25-50 cm) was significantly greater than that of IR64, suggesting that Dro1 plays a crucial role in increased deep rooting under upland field conditions.

TAM 04 O‐16L Long‐Staple Upland Cotton with Improved Strength

TAM 04 O‐16L (Reg. No. GP‐926, PI 659441) upland cotton (Gossypium hirsutum L.) germplasm line was developed by the Cotton Improvement Laboratory, Department of Soil and Crop Sciences, Texas AgriLife Research, Texas A&M University, and released in 2009 as part of an ongoing effort to create germplasm with combinations of improved fiber quality parameters, especially upper half mean length (UHML) and fiber bundle strength (FBS). TAM 04 O‐16L exhibited high volume instrument UHML greater than 32.0 mm in five of six location‐years, which is the minimum UHML to be classified as extra‐long upland cotton according to Cotton Incorporated (Cotton Incorporated, 2009), and in one test TAM 04 O‐16L exceeded the minimum UHML of 34.8 mm for pima (G. barbadense L.). Fiber bundle strength exceeded that of ‘Deltapine 491’ and ‘FiberMax 832’, both of which exhibit excellent FBS among current non‐Acala upland cultivars.

TAM B139–17 ELS Upland Cotton

Extra‐long staple upland cotton (Gossypium hirsutum L.) germplasm lines have been developed by the Cotton Improvement Laboratory, Department of Soil and Crop Sciences, Texas AgriLife Research, Texas A&M University, as part of an ongoing effort to create germplasm and/or cultivars with combinations of improved fiber quality parameters, especially upper half mean length (UHML) and fiber bundle strength. TAM B139–17 ELS (Reg. No. GP‐927, PI 659699) resulted from the cross of TAM 94L‐25 (PI 631440) and PD 6992 (PI 606812). This germplasm line exhibits high volume instrument UHML greater than the minimum for pima (G. barbadense L) combined with fiber bundle strength greater than ‘Fibermax 832’ and other non‐Acala upland cultivars.

Dry Heat and Hot Water Treatments for Disinfesting Cottonseed of Fusarium oxysporum f. sp. vasinfectum.

The potential of low- and high-temperature dry heat, and hot water treatments, for disinfesting cottonseed of Fusarium oxysporum f. sp. vasinfectum was investigated. Naturally infected seeds from Louisiana were air-heated at 30, 35, and 40°C for up to 24 weeks. Seed harvested from bolls inoculated with race 4 of F. oxysporum f. sp. vasinfectum were incubated in dry heat at 60, 70, and 80°C for 2 to 14 days, or were immersed in 90°C water from 45 s to 3 min. The effects on seed germination and vigor of hot water treatment and a subset of the high-temperature dry heat treatments were also examined in seeds of a Pima (Gossypium barbadense) and an Upland (G. hirsutum) cultivar. Low- or high-temperature dry heat did not eliminate Fusarium spp. from the seed, although seed infection declined more rapidly with higher incubation temperatures. High-temperature dry heat treatments effective in eliminating fusaria also significantly reduced seed vigor in both the Pima and Upland cultivars. Seed from all times of immersion in hot water were less frequently infected with Fusarium spp. than nontreated seed. Incidence of seed infection did not differ significantly among immersion times ranging from 75 s to 3 min. Immersion in 90°C water did not reduce germination or vigor at exposure times ≤120 s and ≤150 s for seeds of Pima and Upland cotton, respectively. Results from the hot water treatments suggest that thermotherapy may be optimized to provide a tactic to prevent the spread of virulent F. oxysporum f. sp. vasinfectum genotypes into uninfested areas through infected seed.

Hierarchical classification of switchgrass genotypes using SSR and chloroplast sequences: ecotypes, ploidies, gene pools, and cultivars

Switchgrass (Panicum virgatum L.) is an important crop for bioenergy feedstock development. Switchgrass has two main ecotypes: the lowland ecotype being exclusively tetraploid (2n = 4x = 36) and the upland ecotype being mainly tetraploid and octaploid (2n = 8x = 72). Because there is a significant difference in ploidy, morphology, growth pattern, and zone of adaptation between and within the upland and lowland ecotypes, it is important to discriminate switchgrass plants belonging to different genetic pools. We used 55 simple sequence repeats (SSR) loci and six chloroplast sequences to identify patterns of variation between and within 18 switchgrass cultivars representing seven lowland and 11 upland cultivars from different geographic regions and of varying ploidy levels. We report consistent discrimination of switchgrass cultivars into ecotype membership and demonstrate unambiguous molecular differentiation among switchgrass ploidy levels using genetic markers. Also, SSR and chloroplast markers identified genetic pools related to the geographic origin of the 18 cultivars with respect to ecotype, ploidy, and geographical, and cultivar sources. SSR loci were highly informative for cultivar fingerprinting and to classify plants of unknown origin. This classification system is the first step toward developing switchgrass complementary gene pools that can be expected to provide a significant heterotic increase in biomass yield.

Differential Growth and Carbohydrate Usage in Switchgrass Ecotypes under Suboptimal Temperatures

ABSTRACTSwitchgrass (Panicum virgatum L.) is widely adapted throughout North America, but its productivity tends to decline with increasing latitude. Little is known about its genetic potential to photosynthetically acclimate to suboptimal growth temperature, although such potential could be useful to enhance productivity. To examine this, a growth chamber study was conducted with two lowland (Alamo and Kanlow) and two upland (Cave in Rock and Sunburst) ecotypes grown under day/night air temperatures of 32/24°C and later switched to 22/14°C. Photosynthesis, growth, and carbohydrates were analyzed before and after temperature switching. Photosynthesis was greater in lowland than upland cultivars at 32°C air temperature. After switching to 22/14°C and allowing plants to adjust, photosynthesis declined with little difference among cultivars. Moreover, photosynthetic capacity among cultivars slightly decreased or remained similar compared to before the temperature switch. However, after switching to 22/14°C, Alamo gained the most dry matter (3.9 g plant−1), which was 69, 82, and 152% greater than that of Sunburst, Kanlow, and Cave in Rock, respectively. Total nonstructural carbohydrates increased at 22/14°C, but Alamo showed the least change and no difference in leaf sucrose/starch ratio following the switch. Maintenance of carbon metabolism favoring growth, but not photosynthetic acclimation, may be a key to enhancing switchgrass productivity under suboptimal growth temperatures.

Fine mapping of Sta1, a quantitative trait locus determining stele transversal area, on rice chromosome 9

The stele (root vascular cylinder) in plants plays an important role in the transport of water and nutrients from the root to the shoot. A quantitative trait locus (QTL) on rice chromosome 9 that controls stele transversal area (STA) was previously detected in an F3 mapping population derived from a cross between the lowland cultivar ‘IR64’, with a small STA, and the upland cultivar ‘Kinandang Patong’, with a large STA. To identify the gene(s) underlying this QTL, we undertook fine mapping of the locus. We screened eight plants from BC2F3 lines in which recombination occurred near the QTL. Progeny testing of BC2F4 plants was used to determine the genotype classes for the QTL in each BC2F3 line. Accordingly, the STA QTL Sta1 (Stele Transversal Area 1) was mapped between the InDel markers ID07_12 and ID07_14. A candidate genomic region for Sta1 was defined more precisely between markers RM566 and RM24334, which delimit a 359-kb interval in the reference cultivar ‘Nipponbare’. A line homozygous for the ‘Kinandang Patong’ allele of Sta1 had an STA approximately 28.4% larger than that of ‘IR64’. However, Sta1 did not influence maximum or total root length, suggesting that this QTL specifically controls STA.

Herbicides for Establishing Switchgrass in the Central and Northern Great Plains

Weed interference limits switchgrass (Panicum virgatum L.) establishment from seed. Our objectives were to determine the effect of selected post-plant, preemergence herbicides on stand establishment and subsequent biomass yields of adapted upland switchgrass cultivars grown in three environments in the Central and Northern Great Plains. A separate experiment was conducted in eastern Nebraska to determine if there were any differences among switchgrass ecotypes for herbicide tolerance to the optimal herbicide combination. Herbicides applied immediately after planting were different concentrations of atrazine [Aatrex 4L®; 6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], quinclorac (Paramount®; 3,7-Dichloro-8-quinolinecarboxylic acid), atrazine+quinclorac, imazapic {Plateau®; 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-methyl-3-pyridinecarboxylic acid}, and quinclorac+imazapic. Herbicide efficacy was determined by measuring stand frequency of occurrence and biomass yield the year after establishment. The application of quinclorac plus atrazine resulted in acceptable stands and high biomass yields. Imazapic often reduced switchgrass stands in comparison to the nontreated control and is not recommended for switchgrass establishment. In the multi-state trials, the herbicide by cultivar interaction was not significant for stands or biomass yields, indicating that the effects of herbicides on switchgrass stands and biomass yields were consistent over the upland cultivars used in the trials. No differences were detected among switchgrass lowland and upland ecotypes for tolerance to atrazine and quinclorac. Quinclorac, which provides effective control of grassy weeds, and herbicides such as atrazine which provide good broadleaf weed control are an excellent herbicide combination for establishing switchgrass for biomass production in the Great Plains and the Midwest.

Irrigated cotton in the tropical dry season. II: Biomass accumulation, partitioning and RUE

Growing cotton during the tropical dry season avoids many insect pests endemic in the wet season. The impact of low mid-season radiation and night temperature that characterise the dry season, on the conversion of radiation to biomass (RUE) and the partitioning of this biomass were measured as these were largely unknown. Over three seasons, two Gossypium hirsutum (upland) cultivars and a Gossypium barbadense cultivar were sown from March to June at the Ord River (15.5°S), Western Australia. For the highest yielding March and April sowings, final biomass was similar to high yielding temperate grown cotton (∼30° latitude) and was generally greater than May or June sowings. However, biomass was accumulated differently: maximum growth rate was 6–12 g/m 2/day for 78–134 days compared with 15–25 g/m 2/day for 25–60 days reported for temperate grown cotton. RUE changed significantly with ontogeny, peaking between squaring and early flowering. The range in RUE of 1.2–2.0 g/MJ throughout the crop lifecycle for the upland cultivars was similar to temperate climates where biomass was corrected to a glucose equivalent. The RUE of 1.2–2.3 g/MJ measured over the lifecycle of G. barbadense cultivar was the first reported for this species. From first square to first flower the variation in RUE could be explained by a linear decline ( p < 0.05) with temperature, which may limit vegetative biomass in May and June sowings and in cooler than average seasons for March and April sowings. Due to favourable temperatures and water supply, sowing in March would have the greatest risk of rank growth. It was concluded the low temperature and radiation during flowering and boll growth combined to reduce crop growth rate but high yields were achieved when the crop boll filling phase was extended. Management must be tailored to ensure a high proportion of boll growth (60–80%) can occur after vegetative growth has terminated.

Irrigated cotton in the tropical dry season. I: Yield, its components and crop development

Growing cotton during the dry (winter) season avoids many insect pests endemic in the wet season (summer) and could permit the reintroduction of cotton to the semi-arid tropics in Australia. This research addressed the questions: (1) what yield is possible given the lower mid-season radiation and temperature of the dry season, (2) the prediction and management of crop development using a range of sowing months to assess whether cotton can be grown and picked within the dry season. Over three seasons two Gossypium hirsutum L. (upland) cultivars and one Gossypium barbadense L. cultivar were sown from March, to June at the Ord River (15.5°S) in Western Australia. For the upland cultivars, lint yields of 1900–2300 kg/ha for March and April sowings were at the high end of Australian and International benchmarks. High lint yields were linearly correlated with a greater proportion of bolls that were located on outer sites on fruiting branches than for high yielding crops in temperate climates (∼30°lat.). The change in boll position increased the length of the growing season which was also linearly correlated with yield. Future research needs to confirm if low minimum temperatures early in flowering caused the change in boll position and to measure the impact of extreme temperature seasons on yield and time to maturity. The lint yield of the G. barbadense cultivar was highest at a March sowing, at least 87% of the upland cultivars, which is comparable with temperate climates. The frequency of temperatures >35 °C and <11 °C affected time to squaring, requiring modification of existing development models derived in temperate climates. It was concluded sowing during March to April should achieve the dual objectives of high yields and avoidance of rain at maturity. The wide temperature range observed in these experiments improved the prediction of boll period from mean temperature; this function should be applicable outside the semi-arid tropics.

Comparison of Nitrogen Uptake, Transpiration Rate and Exudation Rate between Upland NERICAs and Japanese Cultivars

Our previous study revealed that upland cultivars of New Rice for Africa (NERICAs) exhibited superior biomass production and N uptake compared with selected Japanese cultivars under upland conditions. The objective of this study was to examine whether the N uptake ability of upland NERICAs is attributable to their transpiration and exudation rates. Two NERICA cultivars (NERICA 1 and NERICA 5), two Japanese upland cultivars (Toyohatamochi and Yumenohatamochi), and a Japanese lowland cultivar Hitomebore were grown under rainfed upland conditions at two N levels. The NERICAs exceeded Japanese cultivars in the increment of aboveground dry weight and N content during the ripening stage. The transpiration rate and exudation rate of NERICAs tended to be higher than those of Japanese cultivars during the ripening stage. These results suggest that NERICAs are capable of maintaining higher water uptake ability during the ripening stage, leading to greater N uptake and biomass production at maturity.

Nitrification inhibition activity, a novel trait in root exudates of rice.

Nitrification is an important process in soil--plant systems for providing plant-available nitrate (NO(3) (-)). However, NO(3) (-) is less stable in soils compared with ammonium (NH(4) (+)) and is more easily lost through leaching, runoff or denitrification. This study tested whether biological nitrification inhibition (BNI) activity is present in the root exudates of rice (Oryza sativa) and also the extent of variation between different genotypes. The BNI activity of root exudates was estimated by a bioluminescence assay using a recombinant Nitrosomonas europaea strain. Afterwards, the effect of a single application of concentrated root exudates and that of exudates deposited in the rhizosphere soil was tested on BNI using soil incubation. Soil was added with (NH(4))(2)SO(4) and water to reach 60 % of the water-holding capacity and incubated at 30 °C for different periods. Amounts of NH(4) (+) and NO(3) (-) were determined using a continuous-flow auto-analyser. In an initial screening experiment, BNI activity in the exudates of 36 different rice genotypes was evaluated using a bioassay based on a recombinant Nitrosomonas strain. Significant genotypic variation was detected with the upland cultivar IAC25 demonstrating consistently high BNI activity, while modern lowland varieties like Nipponbare or IR64 exhibited lower activity. Subsequent experiments ruled out the possibility that BNI activity is simply due to non-specific (solute) leakage from roots. Soil incubation studies with concentrated root exudates of IAC25 showed significant reductions in NO(3) (-) formation. This effect was confirmed by detecting lower NO(3) (-) levels in incubation experiments using rhizosphere soil obtained from IAC25. Our results provide first evidence that root exudates of rice can reduce nitrification rates in soil. Having shown this for a model crop, rice, offers possibilities for further exploitation of this phenomenon through molecular and genetic tools.

Growth and Yield of Six Rice Cultivars under Three Water-saving Cultivations

We evaluated the genotypic differences in growth, grain yield, and water productivity of six rice (Oryza sativa L.) cultivars from different agricultural ecotypes under four cultivation conditions: continuously flooded paddy (CF), alternate wetting and drying system (AWD) in paddy field, and aerobic rice systems in which irrigation water was applied when soil moisture tension at 15 cm depth reached −15 kPa (A15) and −30 kPa (A30). In three of the sixcultivars, we also measured bleeding rate and predawn leaf water potential (LWP) to determine root activity and plant water status. Soil water potential (SWP) in the root zone averaged −1.3 kPa at 15 cm in AWD, -5.5 and -6.6 kPa at 15 and 35 cm, respectively, in A15, and −9.1 and −7.6 kPa at 15 and 35 cm, respectively, in A30. The improved lowland cultivar, Nipponbare gave the highest yield in CF and AWD. The improved upland cultivar, UPLRi-7, and the traditional upland cultivar, Sensho gave the highest yield in A15 and A30, respectively. The yields of traditional upland cultivars,Sensho and Beodien in A30 were not lower than the yields in CF. However, the yields of the improved lowland cultivars, Koshihikari and Nipponbare, were markedly lower in A15 and A30. Total water input was 2145 mm in CF, 1706 mm in AWD, 804 mm in A15, and 627 mm in A30. The water productivity of upland rice cultivars in aerobic plots was 2.2 to 3.6 times higher than that in CF, while those of lowland cultivars in aerobic plots were lower than those in CF. The bleeding rate of Koshihikari was lower in A15 and A30 than in CF and AWD, and its LWP was significantly lower in A15 and A30 than in CF and AWD, but Sensho and Beodien showed no differences among the four cultivation conditions. We conclude that aerobic rice systems are promising technologies for farmers who lack access to enough water to grow flooded lowland rice. However, lowland cultivars showed severe growth and yield reductions under aerobic soil conditions. This might result from poor root systems and poor root function, which limits water absorption and thus decreases LWP. More research on the morphological and physiological traits under aerobic rice systems is needed.

Growth and Yield of New Rice for Africa (NERICAs) under Different Ecosystems and Nitrogen Levels

Scarcity of water and N fertilizer are major constraints to rice production, particularly in developing countries where rainfed upland condition dominates. Improvement of genetic adaptability to inadequate water and N fertilizer is one option to maintain productivity in these regions. NERICAs are expected to yield higher under low input conditions, but growth and yield responses of the cultivars to different ecosystems and N levels remain unknown. The objectives of this study were to characterize the growth and yield performance of NERICAs, in comparison with selected Japanese rice cultivars. The two NERICAs (NERICA 1 and NERICA 5), two Japanese upland cultivars (Toyohatamochi and Yumenohatamochi), and a Japanese lowland cultivar Hitomebore were grown under two ecosystems (irrigated lowland (IL) and rainfed upland (RU)) with two N levels (high (H) and low (L)) for two years. The cultivar difference in the aboveground dry weight and grain yield was the largest in the in RU × L plot, where the values of NERICAs were similar to those in the other plots, but the values of other cultivars were substantially reduced. Regardless of cultivar, N contents of the plants at maturity correlated significantly with the aboveground dry weight at maturity, spikelet number and grain yield per area. These results indicate that NERICAs, compared with the selected Japanese upland cultivars that were bred for drought tolerance, have a higher ability to absorb N under upland conditions, which may contribute to higher biomass production and sink formation, resulting in increased gain yield.

Eficiência produtiva de cultivares de arroz com divergência fenotípica

O objetivo do trabalho foi avaliar, fenotipicamente, as cultivares de arroz tradicionais Guarani e Caiapó, e as modernas, CIRAD L(-1)41, Maravilha, BR IRGA 409 e Metica 1, por meio da associação entre os vários componentes da produtividade de grãos, para prover base de seleção genética em populações de plantas. O estudo foi conduzido na estação chuvosa do ano agrícola de 2003-2004, na área experimental da Embrapa Arroz e Feijão, em Santo Antônio de Goiás, GO. Em condições de sequeiro, com suplementação hídrica, as cultivares de arroz de terras altas CIRAD L(-1)41, Guarani, Caiapó e Maravilha, apresentaram maiores índices de colheita e menores percentagens de esterilidade de espiguetas que as de arroz irrigado BR IRGA 409 e Metica 1. Concluiu-se que a maior produção de biomassa pelas cultivares de arroz irrigado não se refletiu na produtividade de grãos. A CIRAD L(-1)41 por apresentar alta área foliar, panículas densas com alto número de grãos e um comportamento intermediário em todos os componentes avaliados, como índice de colheita, massa dos grãos, fertilidade de perfilhos, perfilhamento, esterilidade de espiguetas e taxa de crescimento, produziu 12,5% a mais que a segunda mais produtiva. O aumento do índice de colheita e da massa dos grãos e a redução da esterilidade das espiguetas devido às suas altas correlações com a produtividade, são considerados prioritários em programas de melhoramento de arroz que visem obter cultivares mais produtivas.

Identification of quantitative trait loci for four morphologic traits under water stress in rice (Oryza sativa L.)

Late season drought coinciding with the rice booting to heading stage affects the development of plant height, panicle exsertion, and flag leaf size, and causes significant yield loss. In this study, a recombinant inbred line population derived from a cross between paddy and upland cultivars was used for data collection of the morphologic traits under well water and drought stress conditions. Drought stress was applied at the stage of panicle initiation in the field in 2002 and at the booting stage in PVC pipes in 2003. The data from stress conditions and their ratios (trait measured under stress condition/trait measured under well water condition) or differences (trait measured under stress condition minus trait measured under well water condition) were used for QTL analysis. Totally, 17 and 36 QTLs for these traits were identified in 2002 and 2003, respectively, which explained a range of 2.58%-29.82% of the phenotypic variation. Among them, six QTLs were commonly identified in the two years, suggesting that the drought stress in the two years was different. The genetic basis of these traits will provide useful information for improving rice late season drought resistance, and their application as indirect indices in rice late season drought resistance screening was also discussed.

Relações entre crescimento vegetativo e acúmulo de nitrogênio em duas cultivares de arroz com arquiteturas contrastantes

Foram estudados, mediante análise do crescimento, o acúmulo de biomassa e nitrogênio (N) e sua eficiência de utilização, durante o estádio de crescimento vegetativo, em duas cultivares de arroz (Oryza sativa L.) com arquiteturas contrastantes: IAC-4440, cultivar do grupo moderno para inundação, e Comum Branco, cultivar local rústica de sequeiro. Em experimento com solução nutritiva, foram efetuadas sete coletas, dos 25 aos 85 dias de crescimento, quando foram quantificados a área foliar, a massa seca e o conteúdo de N nas porções vegetativas. A cultivar IAC apresentou maiores valores de biomassa na fase inicial do crescimento, enquanto Comum Branco maiores valores na fase final do experimento. IAC-4440 teve maiores área foliar, área foliar específica e relação raiz: parte aérea do que Comum Branco. As cultivares tiveram o mesmo acúmulo total de N, mas Comum Branco apresentou valores superiores na taxa de assimilação líquida e na taxa de utilização específica de N, indicando melhor utilização do N absorvido. As maiores taxas de crescimento de Comum Branco estiveram associadas aos seus maiores teores de N por unidade de área foliar, mas não aos teores de N por unidade de massa foliar, superiores em IAC-4440. Os resultados indicam que uma cultivar local rústica de arroz pode servir como fonte de eficiência para utilização de N.