Short Cultivars Research Articles

Compreendendo a dinâmica de atributos de cultivares de arroz de ciclo médio e curto sob efeito do nitrogênio

ABSTRACT: Nitrogen (N) is the element supplied by the soil that limits the development of irrigated rice. The hypothesis of the present is that to meet higher demand for N by the plant due to the higher potential yield, it is not necessary to apply a higher dose of N fertilizer. This studyevaluated the efficiency of N utilization, the rate of growth and accumulations of N by plants and the grain yield of two rice cultivars, short cycle and medium cycle, with and without N fertilization. A field experiment was installed in the Rio Grande do Sul, southern Brazil. The treatment factors evaluated were cultivar, with medium and short cycles, with doses of 0 and 150 kg N ha-1. Growth curves, absorption rate, N content and leaf area index over time, root area and grain yield were analyzed. The medium cycle cultivar has a greater potential to explore the environment when compared to the short cycle rice cultivar, both for greater leaf area and root area per cultivation area, as well as for longer exploration times. Thus, the medium cycle cultivar has greater N utilization efficiency and higher grain yield.

A new approach to quantify weed suppression, crop tolerance and weed‐free yield in cereal variety trials without weed‐free plots

AbstractCereal varieties are commonly tested in the presence of weeds in organic agriculture, and a variety of test programmes with weeds are relevant in relation to fields containing herbicide‐resistant weeds. However, the interpretation of results from variety trials with weeds is complex because different levels of weed pressure affect the yield differently. Crop yield is a result of the combined effect of weed suppression, crop tolerance and the weed‐free yield. Until now, there has been no attempt to separate weed suppression, crop tolerance and weed‐free yield in ordinary variety trials without weed‐free plots. This study applied a new approach based on the combination of functional trait analysis and analysis of variance (ANOVA). A total of 16 variety trials were analysed with early crop coverage, final canopy height and disease severity as functional traits. The main objectives were to quantify weed suppression, crop tolerance and weed‐free yield in spring barley varieties, and to evaluate the importance of the trade‐off between weed suppression and weed‐free yield. Results showed that early crop coverage and final canopy height both increased weed suppression, and taller cultivars tolerated weeds better than shorter cultivars. However, a trade‐off between canopy height and weed‐free yield made it difficult to justify the selection of tall varieties unless the weed pressure was at its maximum level in the trials. Large early crop coverage was an advantage in terms of weed suppression and weed‐free yield, making early coverage a better selection criterion than final canopy height under the condition that early coverage is a result of genotypic variation. Future studies have to show how well genotypic and phenotypic variations are related in terms of early coverage and final canopy height.

Genetic Relationships Among Physiological Processes, Phenology, and Grain Yield Offer an Insight Into the Development of New Cultivars in Soybean (Glycine max L. Merr).

Soybean grain yield has steadily increased during the last century because of enhanced cultivars and better agronomic practices. Increases in the total biomass, shorter cultivars, late maturity, and extended seed-filling period are frequently reported as main contributors for better soybean performance. However, there are still processes associated with crop physiology to be improved. From the theoretical standpoint, yield is the product of efficiency of light interception (Ei), radiation use efficiency (RUE), and harvest index (HI). The relative contribution of these three parameters on the final grain yield (GY), their interrelation with other phenological–physiological traits, and their environmental stability have not been well established for soybean. In this study, we determined the additive–genetic relationship among 14 physiological and phenological traits including photosynthesis (A) and intrinsic water use efficiency (iWUE) in a panel of 383 soybean recombinant inbred lines (RILs) through direct (path analyses) and indirect learning methods [least absolute shrinkage and selection operator (LASSO) algorithm]. We evaluated the stability of Ei, RUE, and HI through the slope from the Finley and Wilkinson joint regression and the genetic correlation between traits evaluated in different environments. Results indicate that both supervised and unsupervised methods effectively establish the main relationships underlying changes in Ei, RUE, HI, and GY. Variations in the average growth rate of canopy coverage for the first 40 days after planting (AGR40) explain most of the changes in Ei. RUE is primarily influenced by phenological traits of reproductive length (RL) and seed-filling (SFL) as well as iWUE, light extinction coefficient (K), and A. HI showed a strong relationship with A, AGR40, SFL, and RL. According to the path analysis, an increase in one standard unit of HI promotes changes in 0.5 standard units of GY, while changes in the same standard unit of RUE and Ei produce increases on GY of 0.20 and 0.19 standard units, respectively. RUE, Ei, and HI exhibited better environmental stability than GY, although changes associated with year and location showed a moderate effect in Ei and RUE, respectively. This study brings insight into a group of traits involving A, iWUE, and RL to be prioritized during the breeding process for high-yielding cultivars.

Usage of Bioorganic Nano-fertilizer Nagro as Opportunity of Ecologization for Winter Rye Development (Secale Cereale)

On the basis of research of winter rye productivity dependence of Vlada and Tetra short cultivar from exposure of seed treatment and sowing with bioorganic nano-fertilizer Nagro in Kuznetskaya forest steppe of south-east in West Siberia (2015–2018 years), there was found out increasing of yield activity respectively to control (sowings without fertilizer) for Vlada cultivar – 15-28% and Tetra short – 4-13%. Number of falling increased for 5-23%. Wasn’t spotted correlation between hydrothermal conditions of vegetation and influence of biologics on studied productivity index.

Influence of fertilization on growth and generative parameters of two short day strawberry cultivars grown in substrate, and evaluation of analysing tools for leaf nitrate and potassium

We examined the influence of fertigation on vegetative and generative parameters of strawberry plants (Fragaria × ananassa Duch.) and evaluated rapid analysing tools for N and K in leaf tissue. The experiments were undertaken in an open polytunnel on “table top” with ‘Sonata’ and ‘Korona’ grown in 2-L pots filled with a peat-based soil mixture. The experimental design was a randomized plot with three replications. Plants were fertigated with EC levels of 0.5, 1.0, 1.5 and 2.0 mS cm-1, based on two stock solutions of 7.5 kg YaraLiva™ Calcinit and 7.5 kg Kristalon™ Indigo, both dissolved in 100 L of water. Percentage N and K in leaves differed between analysing methods, cultivars, EC and date. We found interactions between the cultivar and EC level and between date and cultivar for N and K in leaf. Analysing NO(3)- by a photometric method (PM) in a lab, and by Laqua twin (LT), showed significant interaction with N% of leaf dry matter (DM) only for LT (r(2)=0.36). N% increased with higher EC level, more for ‘Korona’ than for ‘Sonata’. LT K+ did not correlate with K% (r(2)=0.014). The number of crowns and runners increased for both cultivars up to EC 1.5, while the number of leaves was unaffected. Petioles were the shortest at the lowest EC. Flower initiation was earlier at low EC in both cultivars. In the following spring, the time to flowering and first harvest was reduced with the decreasing EC. The number of flowers per plant increased up to EC 1.5, but dropped strongly at EC 2.0 for ‘Korona’, while ‘Sonata’ had a gradual increase of flowers with the increasing EC, but the number was only a third of ‘Korona’, except at EC 2.0, where the amount was equal for both cultivars. The conclusion can be drawn that LT correlated better than ChlDualex with N in strawberry leaves. However, r2 was only 0.36 indicating that LT NO(3)- is a coarse management tool. LT K+ was not a promising tool for rapid K+ test in these experiments. ‘Korona’ seemed to benefit of higher N levels for both vegetative growth and generative development than ‘Sonata’ up to EC 1.5, but ‘Sonata’ reached a higher floral primordia development stage in early October.

English

Screening of groundnut (Arachis hypogaea L.) genotypes against spotted pod borer, Maruca vitrata (Geyer) was conducted during rabi 2015-16 at dryland farm, S.V. Agricultural College, Tirupati. Twenty-five genotypes were screened against the spotted pod borer. Among these Percent infestation of M. vitrata was less in K-9, ICGV-86368, TCGS-1426, CS-19 genotypes and more in K-6, Dharani, Narayani and TCGV-1543. The experimental results indicated that spreading type and short stature groundnut cultivars were tolerant to the M. vitrata incidence. Chlorophyll content and Specific Leaf area, these plant physical parameters showed significant effect on incidence of M. vitrata in groundnut crop. Chlorophyll content was negatively correlated with (r =-0.48) with per cent infestation of M. vitrata at 60 DAS. Specific Leaf area was positively correlated with (r=0.43) with per cent infestation of M. vitrata at 60 DAS and also short stature plants groundnut cultivars were tolerant to M. vitrata incidence.

RESPONSE GREEN BEANS TO SPRAY SOME MICRONUTRIENTS AND ADITION ORGANIC FERTILIZER

This experiment carried out at the research station of the College of Agriculture-University of Baghdad during seasons, spring and autumn 2015. Used in agriculture seeds of hybrid primal, one of the short Cultivars. the aim of the experiment study the effect of iron, zinc spray and add organic nutrient in the vegetative growth and plant yield of green beans. The experiment was designed as an experiment factorial 3 * 4 and three blocks according to the experimental design RCBD includes every block 12 treatments resulting from interaction spray four treatments (0, 0.5 Zn ml. L-1water, 2g Fe.L-1 water and Fe + Zn) and add three levels of humic acid (0, 2 and 3) kg ha-1, after melted in a calculated amount of water and insert into the slot around the plants per experimental unit. The results showed the superiority of the treatment of M4 (Fe + Zn) and also the treatment of H2 (3kg ha Humic) in the studied traits As for coefficients interaction has excelled M4H2 by giving altitude plant higher amounted 59.56 and 53.57cm, the number of branches 5.18 and 4.45 branch. Plant-1, leaf area 67.07 and 54.88dm2 plant-1, the concentration of chlorophyll in the leaves were 238 and 248mg. 100g-1 fresh weight, dry weight of vegetative growth were 63.73 and 54.48g. plant-1, the percentage of flour set were 62.00 and 66.67%, one Plant yield 176.70 and 133.99g.Plant-1 for two seasons, spring and autumn every traits sequentially.

Partitioning of Competition for Resources Between Soybean and Corn as Competitor Plant

ABSTRACT Plants compete for resources present below and above the soil surface. The objective of this work was to separate the individual effects of the competition for resources between soybean and corn as competitor plants. The experiment was conducted in a greenhouse, in 2014/2015. The treatments consisted of soybean cultivars (TEC 5718 and TEC 6029) in competition conditions with corn (no competition, competition for soil resources, competition for solar radiation and total competition). The variables evaluated were plant height at 7, 14, 21, 28, 35 and 42 days after emergence (DAE), stem/culm diameter, leaf area, shoot dry mass, root dry mass and the chlorophyll index, at 42 (DAE). The competition for soil resources between soybean and corn is pronounced, being that short cultivars with determinate growth habit, such as TEC 5718, invest more in root biomass, specific leaf area and leaf area ratio when in competition. The soybean cultivars do not suppress corn, but allow it to benefit when associated to its root system, increasing the shoot and root dry mass, leaf area and chlorophyll index.

Identification of bulbing related genes in short day, non vernalization requiring onion

Flowering and bulbing are the most important phenomena in the life cycle of onion and both are driven by the same gene family, the FLOWERING LOCUS T (FT). FT induces bulbing or flowering in response to day length and temperature in onions. Identification and characterization of flowering related genes involved in bulbing was carried out in a short day onion cultivar ('JISL-5') in this study. There are at least 11 FT, one CO and one TFL1 like gene in this short day onion cultivar. The expression patterns of AcFT1, AcFT2, AcFT3, AcFT4, AcFT5, AcFT6 and AcTFL1 during bulbing indicated that AcFT6 might be involved in initiation of bulbing with others like AcFT1, AcFT2 and AcFT3 participating in later stages of bulb enlargement.

Fodder production potential of pearl millet cultivars under marginal environments of Gujarat

Field experiments were carried out at Pearl millet Research Station, Junagadh Agricultural University (JAU), Jamnagar and Grassland Research Station, JAU, Dhari during Kharif 2014, to know the performance of 17 cultivars of fodder pearl millet under marginal environments of Gujarat. Significant differences were observed among the cultivars for days to 50 percent flowering, days to maturity, grain yield and green fodder yield while differences for plant height, plant population and dry fodder yield were non-significant. The locations differences were found significant for all the characters except days to 50 percent flowering and days to maturity. The cultivars x locations differences were reflected non-significant for all the traits except plant height and plant population. Days to 50 percent flowering ranged from 55 days (IP 20611) to 78 days (IP 14753). Days to maturity varied between 84 days (DFMH 30) to 100 days (IP 14294, IP 19415). The cultivar IP 19415 (294 cm) was the tallest cultivar, while, IP 14753 (223 cm) was the shortest cultivar. Grain yield was observed between 5.34 q/ha (IP 20577) to 16.68 q/ha (check PAC 981). Dry fodder yield ranged from 72 q/ha (IP 20611) to 131 q/ha (IP 10437). The cultivar IP 10151 (238 q/ha) produced the highest green fodder yield among all the cultivars followed by IP 20577 (236 q/ha) and IP 10437 (234 q/ha). Thus, these three cultivars viz ., IP 10151, IP 20577 and IP 10437 may be considered for general cultivation under marginal environments of Gujarat.

The suitability of three Galia melon cultivars and different types of cuts for the fresh‐cut industry

Melons (Cucumis melo L.) are widely cultivated in Mediterranean countries. For fresh-cut melon elaboration, factors such as type of cultivar and cut have a significant impact on final product quality. The quality parameters from long, medium and short shelf-life Galia melon cultivars, cut into different shapes such as slices, trapezoids and cylinders and stored up to 10 days at 5 °C, were evaluated in order to learn the suitability of these cultivars and type of cut for minimal processing. In general, long-life melon cultivar had a low respiration rate and ethylene emissions, and high tissue firmness, but low levels of glucose, fructose, vitamin C and flavor rating by consumers. However, despite having higher metabolic activity and susceptibility to microbial spoilage, the short shelf-life cultivar melon had higher firmness retention. This cultivar was characterized by its richness in glucose, fructose and vitamin C, and its sensory quality (flavor) was highly valued. In general, the medium cultivar had an intermediate behavior between long and short cultivars but without their positive attributes. As a consequence of the most intense damage, the cylindrical shape had higher metabolic activity, susceptibility to microbial spoilage and reduced appearance. In the long and medium-life cultivars studied, low flavor was the limiting factor to extend the shelf-life of fresh-cut melon while for the short-life cultivar the limiting factor was its susceptibility to bacterial growth. Cut types such as cylinders should be avoided.

Optimizing triticale sowing densities across the Mediterranean Basin

Triticale and wheat are similar crops, but triticale represents a valuable alternative to wheat due to its greater biomass production and grain yield in Mediterranean-type growing conditions. However, despite the higher yield potential and increasing importance of this crop, there are no dynamic crop models available to assist triticale adaptation via simulation experiments. In a previous study, the APSIM-Nwheat model was parameterized for triticale resulting in a new APSIM-Triticale model but the new model was never compared with detailed experimental triticale data in a one-to-one comparison. Here, the new model was tested with detailed field experimental observations. APSIM-Triticale was able to reproduce phenology, biomass, grain yields and soil water dynamics. The model performed well over several years and management options that included different sowing densities, sowing dates and a short and tall cultivar. The tested model was then used to explore management options to maximize triticale yield across the Mediterranean Basin. The response to sowing density was cultivar and rainfall-environment dependent. The simulation analysis indicated that there was no yield advantage with higher sowing densities with a tall cultivar type in high yielding environments, despite its higher biomass growth rates. The highest yields were achieved at the early sowing date at the sowing densities between 100 and 300plants/m2 in the high rainfall regions for both short and the tall cultivars. The simulation study suggests that sowing a short cultivar with a reduced radiation use efficiency but early vigour growth could increase current yields across different regions, seasons and management options in the Mediterranean climate.

The influence of rice cultivar and sorghum planting date on crop yield in lowland rainfed double cropping systems in Northern Cameroon

Double cropping of rice and dry season sorghum on vertisols can significantly increase cereal availability for farmers both for food security and income generation. The objective of the study was to evaluate the influence of rice cultivar and dry season sorghum planting date on crop yield in lowland rainfed double cropping systems in Northern Cameroon. Over two years, the three rice cultivars evaluated were NERICA 56, SEBOTA 281-2 and SEBOTA 70. These were followed by the local sorghum variety called ‘’Guelendeng’’, sown at three different dates. All rice cultivars were able to grow and provide a yield. Their paddy production was between 5.7 and 7.6 t ha-1. Introducing rice in the rainy season did not hinder the production of subsequent dry season sorghum whose grain yields ranged between 540 and 811 kg ha-1. The choice of rice cultivar has a significant impact on both individual crop yield and the double cropping system yield. However, the need for adequate fertilization for the cereal double cropping system, the availability of short cycle rice cultivars and indicators for the determination of the best transplanting period for dry season sorghum as second crop are main challenges. Key words: Double cropping, lowland rainfed rice, dry season sorghum, transplanted sorghum, vertisols, food security.

CD 150 - short wheat cultivar with high quality and high yield

The industrial quality and lodging resistance of CD 150, a cross between CD104 and CD108, are high and the plant height is short. The average yield was 10 % higher than of the controls in the regions II, III and IV. It is suitable for cultivation in the states of PR, SP, MS and GO, MG, and DF.

Comparative photosynthesis, growth, productivity, and nutrient use efficiency among tall- and short-stemmed rain-fed cassava cultivars

Field trials under rain-fed conditions at the International Center for Tropical Agriculture (CIAT) in Colombia were conducted to study the comparative leaf photosynthesis, growth, yield, and nutrient use efficiency in two groups of cassava cultivars representing tall (large leaf canopy and shoot biomass) and short (small leaf canopy and shoot biomass) plant types. Using the standard plant density (10,000 plants ha-1), tall cultivars produced higher shoot biomass, larger seasonal leaf area indices (LAIs) and greater final storage root yields than the short cultivars. At six months after planting, yields were similar in both plant types with the short ones tending to form and fill storage roots at a much earlier time in their growth stage. Root yield, shoot and total biomass in all cultivars were significantly correlated with seasonal average LAI. Short cultivars maintained lower than optimal LAI for yield. Seasonal P N, across cultivars, was 12% greater in short types, with maximum values obtained in Brazilian genotypes. This difference in P N was attributed to nonstomatal factors (i.e., anatomical/biochemical mesophyll characteristics). Compared with tall cultivars, short ones had 14 to 24 % greater nutrient use efficiency (NUE) in terms of storage root production. The lesser NUE in tall plants was attributed mainly to more total nutrient uptake than in short cultivars. It was concluded that short-stemmed cultivars are superior in producing dry matter in their storage roots per unit nutrient absorbed, making them advantageous for soil fertility conservation while their yields approach those in tall types. It was recommended that breeding programs should focus on selection for more efficient short- to medium-stemmed genotypes since resource-limited cassava farmers rarely apply agrochemicals nor recycle residual parts of the crop back to the soil. Such improved short types were expected to surpass tall types in yields when grown at higher than standard plant population densities (>10,000 plants ha-1) in order to maximize irradiance interception. Below a certain population density (<10,000 plants ha-1), tall cultivars should be planted. Findings were discussed in relation to cultivation and cropping systems strategies for water and nutrient conservation and use efficiencies under stressful environments as well as under predicted water deficits in the tropics caused by trends in global climate change. Cassava is expected to play a major role in food and biofuel production due to its high photosynthetic capacity and its ability to conserve water as compared to major cereal grain crops. The interdisciplinary/interinstitutions research reported here, including an associated release of a drought-tolerant, short-stem cultivar that was eagerly accepted by cassava farmers, reflects well on the productivity of the CIAT international research in Cali, Colombia.

Use of growth retardants in wheat

In general, lodging has been controlled by restricting nitrogen fertilizer application and/or using short cultivars. Growth retardants can also be used to solve this problem.The objective of this study was to evaluate the effect of rates and application times of three growth retardants on Pioneiro wheat cultivar. The trial was carried out in Viçosa-MG, from May to September 2005, in a factorial and hierarchical scheme, in a randomized block design with four replications and a control treatment. The treatments consisted of 500, 1,000 and 1,500 g ha-1 of chlormequat; 62.5, 125 and 187.5 g ha-1 of trinexapac-ethyl and 40, 80 and 120 g ha-1 of paclobutrazol applied at growth stages 6 or 8, growth stage used on the scale of Feeks and Large, and a control treatment without growth retardant application. Only trinexapac-ethyl and chlormequat were efficient in reducing plant height; the effect of chlormequat and paclobutrazol on plant height was independent of the application time, but the trinexapac-ethyl at growth stage 8 produced shorter plant height than at stage 6. Increasing growth retardant rates produced shorter plant heights; chlormequat and paclobutrazol did not affect grain yield. However, the highest trinexapac-ethyl rates reduced wheat yield.

GA 4+7 plus BA enhances postproduction quality in pot tulips

Previously we reported that postproduction quality of pot ‘Seadov’ tulip ( Tulipa gesneriana) was significantly increased by GA 4+7 plus BA in a manner dependent on the concentration and stage of flower development at application. In these experiments, we extended the survey to 20 tulip cultivars to further evaluate the effects of GA 4+7 plus BA sprays for enhancing postproduction flower and leaf quality. The senescence symptom of the cultivars fell into three categories: wilting, wilting-abscission (abscission shortly after tepal wilting) and abscission (abscission without wilting), with the majority of the cultivars belonging to the wilting and wilting-abscission categories. Pots bearing six plants were sprayed with a range of GA 4+7 plus BA concentrations at marketable stage and placed in a simulated consumer environment (SCE). GA 4+7 plus BA significantly enhanced individual flower and postproduction longevity, but the effect was dependent upon the senescence category of the cultivar. In general, GA 4+7 plus BA increased individual flower and postproduction longevity of wilting-type cultivars at concentrations above 10 mg L −1, while longevity of wilting-abscission-type cultivars was only enhanced by 50 mg L −1. Abscission-type cultivars were not affected by any concentrations of GA 4+7 plus BA. Regardless of floral senescence category, leaf yellowing was significantly reduced by GA 4+7 plus BA sprays in those cultivars showing postproduction leaf yellowing. GA 4+7 plus BA did not induce leaf and stem elongation in most cultivars. Only ‘Yellow Baby’, the shortest cultivar, showed elongation of stem and leaf by GA 4+7 plus BA at concentrations above 25 mg L −1. Spray applications of GA 4+7 plus BA can be useful to enhance flower and leaf quality in pot tulips.

Effect of the Rht‐D1 dwarfing locus on Fusarium head blight rating in three segregating populations of winter wheat

AbstractFusarium head blight (FHB) is one of the major fungal diseases in wheat throughout the world. To control FHB severity, breeding genetically resistant varieties is thought to be the most promising strategy. In wheat breeding programmes, short cultivars predominantly carrying the Norin 10 derived semi‐dwarfing allele Rht‐D1b (Rht2) are preferred worldwide because of higher achievable grain yields and lower risk of lodging. This study was conducted to determine the influence of different alleles at the Rht‐D1 locus on FHB reaction. Three winter wheat populations were produced by crossing rather susceptible varieties ‘Biscay’, ‘Pirat’ and ‘Rubens’ carrying mutant‐type allele Rht‐D1b with the more resistant varieties ‘Apache’, ‘Romanus’ and ‘History’ containing the Rht‐D1a wild‐type allele (rht2). The 190, 216 and 103 progeny of the F4‐derived populations were assayed for the presence of Rht‐D1a or Rht‐D1b, plant height, and mean FHB rating after spray inoculation at flowering time with a highly aggressive isolate of Fusarium culmorum. Comparably, high mean FHB severities ranging from 28% to 49% for all population × environment combinations were achieved, with significant genotypic variation for FHB rating and plant height within all populations. Both traits were negatively correlated with r ranging from −0.48 to −0.61 in the complete populations. However, within the subpopulations homozygous for one or other height allele these correlations decreased considerably. The Rht‐D1b semi‐dwarfing allele resulted in 7–18% shorter plants, depending on the population, but a considerably increased FHB reaction of 22–53%. Nevertheless, significant genotypic variance for FHB resistance remained in all tested Rht‐D1b subpopulations indicating that selection for moderately FHB resistant genotypes within agronomically beneficial Rht‐D1b genotypes is still feasible.

Influences of field pea (Pisum sativum) density on grain yield and competitiveness with annual ryegrass (Lolium rigidum) in south-eastern Australia

The variation in field pea grain yield and competitiveness with annual ryegrass due to crop density, row spacing and cultivar was determined to enable farmers to better manage weeds with cultural control tactics. Crop density varied with seeding rate, cultivar, row spacing and year. Higher seeding rates were required to reach equivalent plant densities in cv. Dinkum (short, semi-leafless) compared with cv. Dundale (tall, conventional-leaf), and at 36 cm compared with 18 cm row spacing. Field pea grain yield was reduced more at low crop densities, in Dinkum, at 36 cm row spacing, and in the presence of weeds. Percentage yield losses from weed competition were similar in both cultivars (about 70–80%) at a low density of 10 plants/m2 in 2 seasons. At higher crop densities Dinkum had a larger loss than Dundale (i.e. at 30 plants/m2 losses were 60 and 35%, respectively, compared with 50 and 5% at 60 plants/m2). Seasonal variation influenced the effect of crop density on yield loss from weeds. The percentage yield loss from weeds in 1993 ranged from about 90 to 40% at plant densities of 10 to 40 plants/m2, in contrast to 1995 when 40% yield loss occurred at all these densities. Ryegrass dry weight was reduced with increasing field pea density in both years, and in the tall more than the short cultivar in 1 year. Maintaining recommended field pea seeding rates has considerable financial benefits in both weed-free (around $100/ha) and weed-affected crops (to $400/ha). In weedy situations, integrating cultural practices such as higher seeding rates and choice of cultivar that enhance crop competitiveness will improve weed management in south-eastern Australia.

Role of gibberellic acid in cotton fibre development

Fibres of three cotton cultivars (Gossypium hirsutum H-4, H-8 and G. arboreum G. Cot-15) were analysed for growth in terms of fibre length and dry weight and endogenous gibberellic acid (GA3) content thrice during 1997–2000, at Rajkot. The development of cotton fibre was divided into four distinct growth phases but overlap between elongation and secondary thickening was considerable which suggests that both these phases are independent of each other. During fibre elongation, GA3 content remained low and increased after a decrease in the rate of fibre elongation in all three genotypes. The long staple cultivar (H-4) showed highest endogenous GA3 content followed by the middle one (H-8) and the short staple cultivar (G. Cot-15). In in vitro studies when GA3, NAA or GA3+NAA was supplemented to the media, increase in fibre length of the short staple cultivar was maximum, followed by the middle one and the long staple cultivar. Both in vivo and in vitro findings suggest that GA3 is one of the important factors that determine fibre length.