Lowland Rice Cultivars Research Articles

Diversidade da virulência de Pyricularia grisea num local de melhoramento genético de arroz

O presente trabalho objetivou estudar a diversidade da virulência de isolados de Pyricularia grisea coletados na Estação Experimental do IAC, Mococa, estado de São Paulo. A composição das raças do fungo e sua compatibilidade com genes de resistência foram estudadas utilizando-se cultivares diferenciais de arroz (Oryza sativa) do Japão. Cinqüenta isolados monospóricos foram obtidos das panículas das cultivares IAC 201 e IAC 4440 afetadas com brusone. As raças JP 137 e JP 177 de P. grisea na cultivar de arroz de sequeiro IAC 201 e a raça JP 200 na cultivar IAC 4440, arroz irrigado, foram identificadas. Foi observada uma baixa freqüência de ocorrência de raças fisiológicas no local de seleção de linhagens de melhoramento. Enquanto todos os 25 isolados provenientes de IAC 4440 foram compatíveis somente ao gene de resistência pi-ta², os isolados de IAC 201 foram compatíveis para sete dos nove genes das diferenciais japonesas. Os resultados mostraram que somente um gene de resistência (pi-z t) foi efetivo a todos os isolados de P. grisea coletados das cultivares de arroz IAC 201 e IAC 4440.

Effects of Plant Growth Regulators on Number of Spikelets per Panicle in Rice(Oryza sativa L.) under Saline Flooding Conditions.

The changes in number of spikelets per panicle (SN) under saline conditions as affected by the application of plant growth regulators were determined. A lowland rice cultivar IR28 whose SN is reduced by salinity was grown in pots filled with the paddy soil and submerged under the three saline solutions of 50 mM, 100 mM and 150 mM sodium chloride (NaCl) and tap water during panicle development. Indole acetic acid (IAA), kinetin or gibberellin (GA3) (0.5 mM) were foliar-sprayed. Independently, plants were grown under low solar irradiance (40% to 85% of transmittance) without NaCl application. Control plants were grown with tap water and not subjected to the spray and low solar irradiance. SN decreased because of the occurrence of spikelet malformation and degeneration under saline conditions as a result of only spikelet degeneration under low solar irradiance. The degeneration of spikelets under saline conditions was suppressed by the GA3 spray, though a different type of malformation occurred, resulting in a small SN. The SN decreased in proportion to the decrease of panicle dry weight at panicle emergence with different effects of salinity, GA3 and low irradiance. The effect of the spray of IAA and kinetin was not detectable. From these results, SN decreased under saline conditions because of the occurrence of spikelet malformation as well as the degeneration, and the GA3 spray may suppress the degeneration of spikelets, suggesting that it may alleviate the adverse effect of salinity on SN.

Construção e avaliação do desempenho de três trilhadoras de arroz

Das operações utilizadas no cultivo do arroz, a colheita é uma das mais importantes, seja por seu elevado custo operacional ou porque reflete na produção e na qualidade do produto. Esta operação demanda grande parte da mão-de-obra destinada à produção em pequenas lavouras nas quais, em geral, o trilhamento é realizado manualmente, batendo-se as plantas num anteparo rígido para o desprendimento dos grãos. Este trabalho teve como objetivo construir e avaliar o desempenho de três trilhadoras em cultivares de arroz de várzea e de terras altas. As trilhadoras são dotadas de fluxo intermitente de plantas, acionadas a pedal ou a motor, e de fluxo contínuo de plantas acionadas a motor. Foram trilhadas plantas compridas e curtas, com grãos com diferentes teores de umidade. A trilhadora de arroz de fluxo intermitente de plantas, acionada por motor, apresentou maior capacidade de trilhamento tendo, portanto, melhor desempenho técnico entre as máquinas ensaiadas. As plantas com colmos curtos, em relação às de colmos compridos, proporcionaram maior rendimento no trilhamento.

Submergence tolerance of rainfed lowland rice: search for physiological marker traits

The submergence tolerance of four rainfed lowland rice (Oryza sativa L.) cultivars was evaluated after submergence in a natural water pond for different submergence durations (0, 7, 11, and 15 days). Complete submergence of plants induced elongation and accumulation of volatile aldehydes at different rates in the cultivars studied. Total soluble carbohydrates (TSC) and starch content, on the other hand, decreased during submergence. Plant survival recorded after 10 d of desubmergence showed large cultivar differences. Plant elongation during submergence has been found to be negatively correlated with survival (r = -0.77), emphasizing the importance of reduced elongation growth during submergence. Higher amounts of starch and total soluble carbohydrate (TSC), before and at the end of submergence period, greatly improved the survival during submergence and recovery growth after desubmergence. Aldehyde content was measured in the shoots as an indicator of the shift in metabolic activity from aerobic respiration to anaerobic fermentation, which differed in tolerant and intolerant cultivars. Intolerant cultivars invariably produced more aldehydes than tolerant ones. Aldehyde production rate was negatively correlated with plant survival, suggesting that plants utilizing excess energy reserve during submergence stress suffered the most, resulting in poor survival. Our results suggest that greater elongation growth during submergence has pronounced adverse effects on rice plant survival during submergence, and that higher initial carbohydrate (soluble sugar and starch) enable rice plants to sustain submergence stress and regenerate quickly after desubmergence. These findings are discussed in relation to adaptation traits for submergence tolerance in rainfed lowland rice.

Macro‐ and micronutrients removed by upland and lowland rice cultivars in West Africa

Plant analysis is an important component of soil fertility and plant nutrition research. Plant analysis at harvest of the crop forms the basis for constructing nutrient balances and assessing the nutrient needs of production systems. Amounts of macro‐ and micronutrient elements removed by improved, upland and lowland rice cultivars were determined in field experiments at two sites in Ivory Coast. Amounts of nitrogen (N), zinc (Zn), and manganese (Mn) removed for 11 rice grain yield by upland and lowland rice cultivars were similar, but the amounts of phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) removed were higher for lowland than upland rice. The nutrient element harvest indexes (amount in grain/amount in grain plus straw) varied between the cultivars, but more importantly, among nutrient elements. On average the nutrient harvest index was highest for P (69%) and lowest for K (10%). The results suggest that the nutrient requirement of rice for K can be met to a large extent through the recycling of K in rice straw. The amounts of other major nutrients, N and P in the straw were small and hence less scope for supplying these nutrients through the recycling of rice straw.

Endodermal silicification in developing seminal roots of lowland and upland cultivars of rice (Oryza sativaL.)

Silica deposition in two upland rice cultivars, IRAT 109 and Moroberekan, and one lowland rice cultivar, Koshihikari, were compared. X-ray microanalysis coupled with environmental scanning electron microscopy was used to examine fresh, unfixed, hydrated samples for analyses. The results showed silica deposition in seminal roots exclusively in endodermal cells. A clear basipetal increase in Si content was found in the endodermis of all cultivars. Comparison of silicification intensity between the three cultivars showed higher amounts of Si deposited in the endodermis of upland rice cultivars. This might be related to a higher drought resistance of these types of rice. In leaves, silica deposits were present in all epidermal cells with the highest concentration in silica cells. The amount of Si deposited in leaves was several times higher than in the root endodermis. No relationship between extent of leaf epidermal silicification was found when lowland and upland cultivars were compared.Key words: endodermis, environmental scanning electron microscope (ESEM), rice, root, silica deposits, X-ray microanalysis.

Seasonal differences in iron toxicity tolerance of lowland rice cultivars

Iron toxicity is a major stress and yieldreducing factor in irrigated and rainfed lowlands in West Africa. Varietal tolerance is the most practical and costeffective means of reducing iron toxicity in iron-toxic soils. We have been evaluating lowland rice cultivars for iron toxicity tolerance at Korhogo, Cote d’Ivoire, a site with a consistent and high iron toxicity pressure on plants. Because irrigation water is available, it was possible to evaluate germplasm in both the wet and dry seasons.

Variability and genetics of tolerance for aluminum toxicity in rice (Oryza sativa L.)

A study was undertaken to investigate the variability among lowland rice cultivars and the mode of gene action of aluminum (Al) toxicity tolerance in rice. Pregerminated seeds were grown in a nutrient solution containing 30 ppm Al and in normal nutrient solution, and relative root length (RRL) was determined at the 14-day-old stage to characterize genotypes for tolerance. Sixty-two traditional rice cultivars grown on lowland acid sulfate soil areas of Asia and West Africa were tested. Tolerant varieties 'Azucena', 'IRAT104', and 'Moroberekan', moderately sensitive 'IR29' and 'IR43', and sensitive 'IR45' and 'IR1552' were used to investigate the genetics of tolerance by diallel analysis. Of the 62 cultivars tested, only 3 were found to be sensitive to A l toxicity. Among the tolerant cultivars identified, 11 ('Siyam Kuning', 'Gudabang Putih', 'Siyam', 'Lemo', 'Khao Daeng', 'Siyamhalus', 'Bjm-12', 'Ketan', 'Seribu Gantang', 'Bayer Raden Rati', and 'Padi Kanji') were found to possess higher levels of tolerance than the improved tolerant upland cultivar 'IRAT104'. Diallel analysis revealed that high RRL is governed by both additive and dominance effects with a preponderance of additive effects. The trait exhibited partial dominance, and one group of genes was detected. Heritability was high, and environmenal effects were low. Findings suggest that when breeding for A1 toxicity tolerance, selection can be made in early generations. The pedigree method of breeding would be suitable. Combining ability analysis revealed the importance of both general combining ability (GCA) and specific combining ability (SCA) in the genetics of A1 toxicity tolerance in rice. GCA was more prevalent than SCA. Tolerant parens 'Azucena', 'IRAT104', and 'Moroberekan' were the best general combiners. The presence of reciprocal effects among crosses suggested the proper choice of parents in hybridization programs. Results indicated that 'Azucena', 'IRAT 104', and 'Moroberekan' should be used as the female in crosses for A1 toxicity tolerance.

Drought-stress responses of two lowland rice cultivars to soil water status

The physiological and morphological responses of two semi-dwarf lowland rice cultivars to transient drought were studied in three greenhouse experiments. These responses were related to root-zone soil water status for use in a rainfed-rice simulation model. Results were very similar for both varieties. Drought responses in young plants occurred at a lower soil water status than in older plants. The first observed effect in a drought period in the vegetative phase was a decline in leaf expansion rate compared to well-watered plants. Leaf expansion stopped completely with root-zone soil water pressure potential h in the range −50 to −250 kPa, depending on crop age and growing season. The rate of transpiration, corrected for differences in LAI, remained roughly equal to that of well-watered plants in the range 0 > h > −100 kPa, depending on crop age. As the soil water status declined further, relative transpiration rate decreased with increasing values of log(| h|), following a logistic function. Leaf rolling and early senesence started at h < −200 kPa or lower and were linearly related with log(| h|). Yield differences between plants that were transiently stressed in the early vegetative phase and well-watered plants were not significant. However, flowering and maturity were delayed. Severe drought in the reproductive phase resulted in large yield reductions, mainly caused by an increase in the percentage of unfilled grains and also in grain weight.

Effects of enhanced UV-B radiation on the growth of rice and its susceptibility to rice blast under glasshouse conditions

The effects of enhanced UV-B (280–320 nm) on the susceptibility of 18 irrigated lowland rice cultivars to rice blast ( Pyricularia grisea) were investigated. The rice cultivars were irradiated with UV-B 313 lamps that were either filtered with cellulose acetate of 0.13 mm thickness (light transmission greater than 290 nm) or with Mylar D of 0.13 mm thickness (light transmission greater than 320 nm). Irradiation was for 6 h daily for 21 days starting at 9 days after planting. After irradiation, plants were inoculated with one or two blast isolates. In 18 out of 36 measured interactions the number of lesions per plant was higher in the presence of UV-B than in its absence. However, only two interactions were statistically significant. In a second experiment the dose-response relationship between the cultivars IR30 and IR72 and UV-B was established in the presence and absence of disease. Increasing levels of UV-B significantly reduced leaf areas, dry weights, and heights of both cultivars. Disease severity was either unaffected or decreased by UV-B. However, disease significantly changed the effects of UV-B on plant growth and recovery from UV-B damage. IR30 but not IR72 recovered from UV-B damage in the absence of disease within 5 days. No recovery occurred when inoculated. IR72 suffered even greater reductions of leaf area and dry weight by UV-B when inoculated. Although the effects of UV-B on disease severity may be small, it appears that the tolerance of plants to disease is decreased by UV-B radiation.

Genetic variation detected with RAPD markers among upland and lowland rice cultivars (Oryza sativa L.)

Genetic variation of nine upland and four lowland rice cultivars (Oryza sativa L.) was investigated at the DNA level using the randomly amplified polymorphic DNA (RAPD) method via the polymerase chain reaction (PCR). Forty-two random primers were used to amplify DNA segments and 260 PCR products were obtained. The results of agarosegel electrophoretic analysis of these PCR products indicated that 208 (80%) were polymorphic. All 42 primers used in this experiment were amplified and typically generated one-to-four major bands. Only two primers showed no polymorphisms. In general, a higher level of polymorphism was found between japonica and indica subspecies while fewer polymorphisms were found between upland and lowland cultivars within the indica subspecies. A dendrogram that shows the genetic distances of 13 rice cultivars was constructed based on their DNA polymorphisms. Classification of rice cultivars based on the results from the RAPD analysis was identical to the previous classification based on isozyme analysis. This study demonstrated that RAPD analysis is a useful tool in determining the genetic relationships among rice cultivars.

Host Range, Mating Type, and Fertility ofPyricularia griseafrom Wheat in Brazil

Isolates of Pyricularia grisea collected from wheat in regions of Brazil were inoculated on various gramineous plants to determine their host range. A set of 42 different gramineous plants belonging to nine tribes was analyzed by plant reactions and sporulation potential. The strain from wheat infected gramineous plants of five tribes: Hordeae, Festuceae, Aveneae, Chlorideae, and Agrosteae, but not Japanese differential or Brazilian lowland and upland rice cultivars

Ultraviolet‐B Radiation Effects on Growth and Physiology of Four Rice Cultivars

Enhanced ultraviolet‐B (UV‐B, 280–320 nm) radiation, such as could be caused by stratospheric O, depletion, has been demonstrated to profoundly affect plants. This study was conducted to determine the effects of UV‐B on four high‐yielding, lowland rice (Oryza sativa L.) cultivars (IR30, IR45, IR64, and IR74), and to evaluate morphological and physiological parameters for identifying sensitive and less‐sensitive genotypes in future screenings. Ultraviolet‐B radiation was supplied by UV‐B–emitting fluorescent lamps in the phytotron. Plant height, leaf area, dry weight, net assimilation rate (NAR), and relative growth rate (RGR) were significantly influenced by 4‐wk UV‐B treatment in some cultivars. Based on the relative change in total biomass production between UV‐B‐irradiated and control plants, cultivar IR74 was the most sensitive and cultivar IR64 the least sensitive. Biomass production, however, did not proportionally decrease with plant height under UV‐B treatment. Changes in plant height and leaf area induced by UV‐B can alter the rice plant canopy structure. Differential varietal response was found in shoot dry weight, leaf area, specific leaf weight (SLW), NAR, and RGR. These parameters can be used as selection criteria for rice cultivars less sensitive to UV‐B. Most physiological and biochemical parameters evaluated, including root‐oxidizing activity, soluble protein, nucleic acid, ion leakage, stomatal aperture, and flavonoid and chlorophyll contents, were affected by 2 wk of UV‐B treatment and gave differential cultivar responses. The distinct responses and relative ease in measurement of stomatal opening and ion leakage make these parameters suitable indices in selecting rice cultivars less sensitive to UV‐B after 2 wk of UV‐B treatment.

Five Lowland Rice Cultivars Released in Turkey

Five Lowland Rice Cultivars Released in Turkey

Leaf Age Related Partial Resistance toPyricularia oryzaein Tropical Lowland Rice Cultivars as Measured by the Number of Sporulating Lesions

To study the effects of leaf age on resistance, plants of four rice cultivars were inoculated with a virulent isolate of Pyricularia oryzae. Susceptibility of leaves declined rapidly with increasing leaf age. In older leaves, fewer sporulating lesions developed per unit of leaf area, and eventually leaves became completely resistant. The period during which newly formed leaves were susceptible, as well as the initial level of susceptibility of new leaves, differed greatly between cultivars. Cultivars with high levels of partial resistance to leaf blast showed typical susceptible lesions, but the resistance in leaves rapidly increased with age, and the initial level of susceptibility of new leaves was low

Tolerância a alumínio e eficiência a fósforo em milho e arroz: características independentes

Oito experimentos foram realizados em solução nutritiva, em casa de vegetação localizada no Centro Experimental do Instituto Agronômico de Campinas, em 1982-86, com o objetivo de avaliar cem linhagens de arroz e quarenta de milho quanto à eficiência e utilização de fósforo na ausência de Al, e quanto à tolerância a Al em baixo P. Verificou-se, através de coeficiente de correlação (r), se a tolerância a Al se relacionava com a eficiência a P, avaliadas por parâmetros confiáveis previamente estabelecidos. As linhagens de arroz e milho foram agrupadas em nove classes cujos limites foram determinados pelo intervalo de confiança da média do índice de eficiência a P e da média do índice de tolerância a Al. As linhagens de arroz de sequeiro mostraram-se superiores quanto à tolerância a Al, e as de arroz irrigado, quanto à eficiência a P. Dez linhagens de arroz de sequeiro e cinco de arroz irrigado foram selecionadas como eficientes a P e tolerantes a Al. As linhagens de milho tenderam a uma inversão nos índices de avaliação das duas características, sendo três selecionadas como altamente tolerantes a Al, mas intermediárias quanto à eficiência a P. Para o material genético de arroz e milho, os coeficientes de correlação (r) entre os respectivos índices indicaram que as referidas características são independentes nas plantas.

Lowland rice response to potassium fertilization and its effect on N and P uptake

Not much is known about the response of lowland rice to K fertilization under Brazilian conditions. A field experiment was conducted during four consecutive years to determine the response of three lowland rice (Oryza sativa L.) cultivars to K fertilization on a Low Humic Gley soil. In the first two years, K was broadcast at rates of 0, 42, 84, 126, and 168 kg K ha−1. In the last two years K rates were reduced to 0, 25, 50, 75, and 100 kg K ha−1 and applied in a band. Potassium significantly (P < 0.01) increased grain yields but the response varied from cultivar to cultivar and year to year. Yield responses to K fertilization were superimposed on a general trend of increasing grain yields across the four growing seasons. Mean grain yields increased 14.3% with broadcast application of K in the first two years and 10.4% with banded application of K in the last two years when compared to the control treatments. Extractable soil K increased with K application rate and decreased with soil depth. Potassium was rapidly removed from the soil and yearly broadcast or banded application of K can be expected to result in a significant increase in grain yield of lowland rice in these soils.

Performance of Promising Rainfed Lowland Rice Cultivars in West Bengal

Performance of Promising Rainfed Lowland Rice Cultivars in West Bengal

Tolerance of Rainfed Lowland Rice Cultivars and Breeding Lines for Submergence At Seedling Stage

Tolerance of Rainfed Lowland Rice Cultivars and Breeding Lines for Submergence At Seedling Stage

Leaf and Neck Blast Resistance in Tropical Lowland Rice Cultivars

The classification of neck blast resistance of intermediate and susceptible lines varied between trials, mostly due to differences in flowering date. The mean leaf blast values from the miniplot trials were positively correlated with the mean neck blast values from the lowland trials. Some lines, however, were exceptions to this general relationship. Lines of particular interest to breeders should be screened for neck blast resistance; improved methods are required, particularly for neck blast testing