Boot Leaf Stage Research Articles

Effect of NPK and Growth Regulators on Growth and Productivity of Wheat (Triticum aestivum L.)

The present study highlights the effect of NPK and growth regulators on growth and productivity of wheat (Triticum aestivum L.). Wheat is one of the most important and widely grown food crops with over 25000 different cultivars. The exploration was carried out during Rabi season 2021-22 at Instructional farm, BTC College of Agriculture and Research station, Bilaspur (C.G.). The soil of the experimental site was clayed in texture. The wheat (Var. HI-1544) was grown and treatments were replicated three times in randomized block design. The experiment consists of twelve treatments The crop was sown on 11 November, 2021 and harvesting was done on 24 March 2021.The result that higher grain (45.55 q ha-1) and straw (46.45 q ha-1) yield were observed under the treatment 150% RDF + Two spray of growth regulator at first node(35 DAS) & boot leaf stage (60 DAS) (T9). The improvement in yield of wheat was recorded with the application of 150% RDF + Two spray of growth regulator at first node(35 DAS) & boot leaf stage (60 DAS) (T9) which was at par with the application of 150% RDF (T6). Treatment (T9) assigned yield advantage of 21.19% and 21.52% in grain and straw yield respectively as compared to 150% RDF (T6) and Absolute control (T1). The result of the present study came to the conclusion that the application of 150% RDF+ growth regulators through fertilizer is essential to get higher production output and profit from wheat cultivation and reduce the risk.

Effect of NPK and Growth Regulators on Yield Attributes of Wheat (Triticum aestivum L.)

The present experimental study was carried out during Rabi season 2020-21 at Instructional farm, BTC College of Agriculture and Research station, Bilaspur (C.G.). The soil of the experimental field was clay in texture. The wheat Var. HI-1544 was grown and treatments were replicated three times in randomized block design. The experiment consists of nine treatments The crop was sown on 11th November, 2020 and harvesting was done on 24th March, 2021.The result revealed that maximum yield parameters the significantly higher grain (45.55 q ha1) and straw (46.45 q ha-1) yields were observed under the treatment 150 % RDF NPK + Two spray of growth regulator at first node (35 DAS) and boot leaf stage (60 DAS) (T9). Further, among the nutrient management treatment, significantly maximum grain and straw yield up to (43.65q ha-1) and (46.35q ha-1) respectively were recorded under150 % RDF NPK (T6). However, the treatment (T9) was statically similar with the treatment (T6). The improvement in yield attributes and yield of wheat was recorded with the application of 150 % RDF NPK + Two spray of growth regulator at first node (35 DAS) and boot leaf stage (60 DAS) (T9) which was at par with the application of 150 % RDF NPK (T6). Treatment (T9) assigned yield advantage of 21.19 % and 21.52 % in grain and straw yield respectively as compared to 150 % RDF NPK (T6).

Assimilate Partitioning and Photosynthetic Parameters of Rice (Oryza sativa L.) in Response to Salicylic Acid Application

Salicylic acid (SA), a signaling molecule is known to affect various physiological processes like growth and development, photosynthesis, absorption and translocation of assimilates etc. Therefore, an experiment was conducted to study the effect of salicylic acid on assimilate partitioning and yield of rice. The experiment comprised of 14 treatments replicated thrice in Randomized Complete Block Design (RCBD). Foliar application of SA @ 50, 100, 150 & 200 µg ml-1 was done at boot leaf stage (BL), one week after boot leaf stage (1WABL) and at BL + 1WABL. Treatment of water spray and unsprayed (control) were also included. Findings reveal that application of 100 µg ml-1 SA at BL + 1WABL resulted in the highest grain yield, which was statistically similar to 150 µg ml-1 SA at BL + 1WABL. The higher productivity under respective treatments can be ascribed to higher crop growth rate, relative growth rate, net assimilation rate and improvement in partitioning of dry matter from vegetative parts to grains due to improved vascularization. Also there was improvement in photosynthetic efficiency in terms of total chlorophyll content; carotenoid content and Hill reaction activity under SA treated plots. Thus, the productivity enhancement in rice can be achieved through 2 foliar sprays of salicylic acid @ 100 µg ml-1 each at boot leaf stage + one week after boot leaf stage.

Diversity of Major Predators Under Different Insecticide Regimes in Two Important Growth Stages of Rice

The effect of twelve different groups of insecticides on diversity of major predators (insects and spiders) during active tillering and bootleaf stage of rice crop was evaluated in West Bengal. The results showed that spinosad, emamectin benzoate, sulfoxaflor and pymetrozine were highly safe while buprofezin, imidacloprid, indoxacarb and chlorantraniliprole were moderately so. The insecticides like lambdacyhalothrin, fipronil and chlorpyriphos were found to be toxic. During active tillering stages the predator diversity was maximum in emamectin benzoate treatment and least in case of lambdacyhalothrin. Similar trend was observed for evenness index in the emamectin benzoate and lambdacyhalothrin. During boot leaf stage, Shannon index was maximum in sulfoxaflor and minimum in lambdacyhalothrin. Overall, insecticidal treatments resulted in decrease in diversity of predators during both stages of rice crop.

Effect of boron on growth indices, physiological traits and productivity of rice (Oryza sativa) under north-west Indian conditions

An experiment was conducted during the rainy season (kharif) of 2019 at the Punjab Agricultural University, Ludhiana, to explore the role of boron (B) in improving seed filling, vascularisation and yield of rice (Oryza sativa L.). The field experiment comprising 14 treatments, viz. foliar application of boron (B) @ 24, 28, 32 and 40 millimolar (mM) at boot-leaf stage (BL) or at 1 week after boot-leaf stage (1 WABL) as well as at both the stages (BL+1 WABL) along with foliar application of water and control (unsprayed), were laid out in randomised complete-block design, with 3 replications. Plants sprayed with 24 mM B at different stages showed improved photosynthetic efficiency in terms of chlorophyll content, carotenoid content and hill-reaction activity of leaf chloroplasts. Also, the yield-attributing traits, viz. 1,000-grain weight, panicle weight and panicles/m2, were significantly higher in plants treated with 24 mM B at BL + 1 WABL, followed by plants treated with 24 mM B at 1 WABL, which were similar to that treated with 24 mM B at BL or at 1 WABL. Increasing B concentration above 24 mM showed negative impact on the growth and yield of rice. Thus, foliar spray of 24 mM B at BL or 1 WABL may be used to improve the productivity of rice.

Performance and nitrogen use efficiency of grain sorghum through method and time of nitrogen application under semi-arid environment

The present field investigation was carried out for three consecutive kharif season of 2015, 2016 and 2017 at research farm of Agricultural Research Sub Station Diggi, Tonk to improve nitrogen use efficiency through method and time of nitrogen application and performance of sorghum under semi arid environment of Rajasthan, India. The experiment was laid out in factorial randomized block design consisted of five nitrogen scheduling treatments viz. N1 (50+50), N2 (50+25+25), N3 (25+50+25), N4 (25+50+15+10), N5 (25+45+5+15+10), and two genotypes viz CSH-16 and CSV-20 and replicated thrice. The results revealed that the application of nitrogen with 50% N at sowing + 25% N at 30 DAS + 25% N at boot leaf stage recorded significantly maximum plant height and dry matter accumulation of sorghum. The application of nitrogen with 25% N at sowing + 50% N at 30 DAS + 15% N at boot leaf stage+10% at Grain filling stage recorded minimum plant height and dry matter accumulation of sorghum. The significantly maximum number of grains/cob (3136.3) and test weight (28.0 g) were registered with application of nitrogen with 50% N at sowing + 25% N at 30 DAS + 25% N at boot leaf stage. However, crop supplied nitrogen with the 50% N at sowing + 50% N at 30 DAS recorded statistically similar results for these yield attributes. The grain, stover and biological yields of sorghum due to different method and time of nitrogen application treatments were found statistically at par. The application of nitrogen with 50% N at sowing + 25% N at 30 DAS + 25% N at boot leaf stage resulted in increased mean gross return (Rs. 89159). Among the method and time of nitrogen application treatments, the highest cost of cultivation (₹26301), gross returns (₹89159) net returns (₹62858) and B:C ratio (2.39) were recorded with application of nitrogen with 50% N at sowing + 25% N at 30 DAS + 25% N at boot leaf stage. The experimental results supported the hypothesis that nitrogen use efficiency could be improved by method and time of nitrogen application. Proper method and time of nitrogen application have positive impact on growth, productivity and profitability of grain sorghum. Thus, it is concluded that improvement of nitrogen use efficiency through method and time of nitrogen application can be advocated as sustainable strategy for enhancing productivity and profitability of sorghum cultivation under semi arid environment.

Effect of Nitrogen Scheduling and Cultivars on Yield Attributes and Yields of Sorghum (Sorghum bicolor L.)

A field experiment was conducted during kharif season of 2013 at Udaipur (Rajasthan) to find out the effect of nitrogen scheduling and cultivars on yield attributes, yield and soil fertility status after harvest of sorghum. Treatment consisted two cultivars (V1: CSH 16 and V2: CSV 20) and five nitrogen schedules (N1: 50% at sowing as basal + 50% at 30 DAS, N2: 50% at sowing as basal + 25% at 30 DAS + 25% at boot leaf stage, N3: 25% at sowing as basal + 50% at 30 DAS + 25% at boot leaf stage, N4: 25% at sowing as basal + 50% at 30 DAS + 15% at boot leaf stage + 10% at grain filling stage, N5: 25% at sowing as basal + 45% at 30 DAS + 5% foliar spray at 45 DAS + 15 % at boot leaf stage + 10% at grain filling stage) were assigned in a factorial randomized block design. The results revealed that the cultivar CSH 16 recorded significantly higher number of grains per panicle, 1000 grain weight, grain yield (1521 kg/ha), harvest index (13.17) and nitrogen content in plant, whereas significantly higher number of primaries per panicle, stover yield (11141 kg/ha) and available nitrogen in soil were recorded in CSV 20. Application of nitrogen in N2 schedule (50% at sowing as basal + 25% at 30 DAS + 25% at boot-leaf stage) had marked influence on yield attributes, yield and nitrogen content in plant when compared to rest of the nitrogen schedules. Therefore, it was concluded that significantly higher grain yield was recorded in cultivar CSH 16 and N2 schedule of nitrogen application from sorghum.

Growth parameters of autumn rice under various irrigation schedules and nutrient management

A field experiment was conducted at Instructional-cum-Research (ICR) Farm, Assam Agricultural University, Jorhat-13 during autumn season of 2015 to study the nutrient management of direct seeded autumn rice under various irrigation schedules. The experiment consisted of four irrigation schedules viz., I1(No irrigation), I2(Irrigation at tiller initiation (TI) + boot leaf stage (BL)), I3(Irrigation at TI + panicle initiation (PI) + BL), I4 (Irrigation at TI + PI + Grain filling stage(GF)) and three nutrient management practices viz.,F1(100 % RDF +2t/ha FYM), F2(50 % RDF +1.5 t/ha enriched compost), F3(50 % RDF + 1.5 t/ha Vermicompost). The trial was laid out in split plot design with three replications. The soil was sandy loam. Inglongkiri rice variety was used in the experiment. Results revealed that irrigation schedule I3(Irrigation at TI + PI + BL) recorded significantly the highest growth characters of rice in terms of plant height, number of leaves per plant, and dry matter accumulation. Different nutrient management practices brought about significant differences in plant population per and dry matter accumulation. The highest of these parameters were recorded under application of 50% RDF along with 1.5 t/ha enriched compost and this was statically at par with F1 (100% RDF +2 t/ha FYM).

Evaluation of bio inoculants fortified Lignite Fly Ash (LFA) against sheath blight (Rhizoctonia solani Kuhn) and sheath rot (Saracladium oryzae (Sawada) Games and Haksworth) diseases of rice in Cauvery delta region of Tamil Nadu

Sheath blight and sheath rot are the major diseases of rice in Tamil Nadu particularly in Cauvery delta region. Pot culture and field trials were conducted to evaluate the efficacy of consortia application of ecofriendly components viz., Fortified Lignite Fly Ash (LFA), Annamalai Mixture and antagonistic microorganisms against the sheath blight and sheath rot diseases and yield parameters during the kuruvai and samba season of 2016. Among the different combination of ecofriendly components, combined application of Pseudomonas fluorescens and Bacillus subtilis as seed treatment@ 10g/kg of seed, soil @ 10 kg/ha at transplanting, foliar spray @ 10 kg/ha at tillering and boot leaf stage plus spraying Annamalai Mixture @ 20 lit /ha at tillering stage and boot leaf stage plus Fortified lignite fly ash as soil @ 40 kg/ha at transplanting and foliar dust @ 30 kg/ha at boot leaf stage significantly reduced sheath blight and sheath rot disease incidence in pot culture and field condition. The same treatment recorded the maximum grain yield. All the ecofriendly components treated plants significantly decreased the diseases incidence and increased the grain yield as compared to control.

Evaluation of endophytic biocontrol agents against sheath rot of rice

For the evaluation of endophytic biocontrol agents against sheath rot of rice an study was conducted with bacteria to find its efficacy against S. oryzae. In vitro efficacy of endophytes was evaluated and mode of action of endophytes were identified for its disease control ability. In field study the application of Seed bacterization (SB) + Seedling root dip (SRD) + Foliar spray with Endophytes @ 2.5 kg/ha at milky and boot leaf stage recorded the minimum sheath rot incidence of 72.18% compared to 60.73% in control.

Genetic analysis of epicuticular wax (bloom) locus in sorghum

The inheritance pattern of epicuticular wax (bloom) locus in F1 and F2 generations of seven sorghum crosses involving a bloomless mutant, RS647 and bloom sorghum parents was studied during the post-rainy season of 2012-13. The plants were scored for bloom and bloomless expression at boot leaf stage. The study revealed that the five crosses BTx623 × RS647, 27A × RS647, 296A × RS647, RS647 × Swathi and IS22380 × RS647 segregated in 3 (bloom): 1 (bloomless) indicating the monogenic control of bloom locus in these crosses. The F2 of the cross Phule Maulee × RS647 showed a di-genic ratio of 13 (bloom):3 (bloomless) while RS647 × M35-1 cross segregated with 9 (bloom):7 (bloomless) di-genic ratio. The study indicated that the bloom expression is under the control of 1-2 genes based on the genetic background of the parents.

English

Experiments were conducted to know the effect of recommended dose of fungicides (Propiconazole, Carbendazim and Hexaconazole), bio-agents and botanicals on incidence and severity of spot blotch disease and seed yield of wheat. Two sprays of Carbendazim at 0.1% at tillering and boot leaf stage resulted in the maximum reduction in spot blotch incidence and severity followed by two applications of Propiconazole at tillering and boot leaf stage. Propiconazole was also found to be quite effective in reducing the level of disease and enhancing crop yield followed by Carbendazim and Hexaconazole. However, Carbendazim, Propiconazole and Hexaconazole were almost equally effective against spot blotch of wheat and may be used as an alternative to each other for management of disease. Two applications of Carbendazim at tillering and boot leaf stages resulted in highest grain yield. Out of the two bio-agents tested against spot blotch of wheat under field conditions, Pseudomonas fluorescence followed by Trichoderma harzianum resulted in the highest reduction in disease incidence. However, both of these bio-agents were comparatively less effective in minimizing the disease as compared to chemical fungicides. Out of four plant extracts two applications of aqueous Eucalyptus leaf extract at tillering and boot leaf stage resulted in the highest wheat yield as compared to other botanical extracts. Key words: Fungicides, bio-agents, Pseudomonas fluorescence, botanicals, Bipolaris sorokiniana, spot blotch, Triticum aestivum.

Seed set variability under high temperatures during flowering period in pearl millet (Pennisetum glaucum L. (R.) Br.)

Pearl millet has recently emerged as a significant irrigated summer season cereal crop in north-western India. But its flowering coincides with air temperatures of ≥40°C, leading to reduced seed set and poor grain yield in most of the available hybrids, although a few hybrids with good seed set and high yield potential are widely cultivated. Under a recent initiative to diversify the genetic base of heat tolerant hybrids, field screening of 221 hybrid parental lines (both B- and R-lines), 53 germplasm accessions and 4 improved populations over four-year period revealed large genetic variability in seed set at daily maximum air-temperature of ≥42°C during flowering. Two locations data on 46 medium maturing genotypes screened during summer 2009 showed that seed set in pearl millet started declining when maximum air temperatures reached 42°C and decreased in curvilinear fashion to 20 percent at 46°C. Similar relationship of seed set with minimum and mean temperature was observed with threshold values of 26.4°C and 34.2°C, respectively. Similarly, the relationship of percent seed set with vapor pressure deficit (VPD) showed threshold value of 6.2kPa for maximum VPD, 1.2kPa for minimum VPD and 3.7kPa for mean VPD. Seed set on 2 each of heat tolerant and susceptible genotypes fitted well on the seed set-temperature response curve for the maximum, minimum and mean air temperatures. Based on 3 to 4 year field screening (2009–2012), five hybrid seed parents (ICMB 92777, ICMB 05666, ICMB 00333, ICMB 02333 and ICMB 03555) and a germplasm accession IP 19877 with 61 to 69% seed set as compared to 71% seed set in a heat tolerant commercial hybrid 9444 (used as a control) was identified. Intra-population variability for heat tolerance was observed in four populations, and highly heat tolerant progenies from two of them were identified. Evaluation of six hybrid parents under controlled environment (maximum temperature of 43°C and minimum temperature of 22°C) revealed boot-leaf stage of pearl millet plant to be more heat sensitive than panicle-emergence stage, and investigations on 6 A-/B-pairs under controlled environment (max. temperature of 44°C and min. temperature of 22°C) revealed female reproductive system of pearl millet to be more heat sensitive than pollen. Comparison of 23 hybrids and their parents for seed set at high air temperature (>42°C) showed heat tolerance as a dominant trait, implying heat tolerance in one parent would be adequate to produce heat tolerant hybrids in pearl millet. Heat tolerant composite developed using identified lines showed high mean seed set under high air temperatures during flowering.

DETERMINATION OF OPTIMUM PHOSPHORUS LEVEL FOR GRAIN SORGHUM USING EXTERNAL AND INTERNAL RESPONSE INDICATORS IN RAINFED SEMI-ARID TROPICAL ALFISOL

The productivity of sorghum, an important staple food crops in semi-arid tropics of the world, is low due to scarcity of moisture and poor soil fertility. Response of crops to phosphorus (P) application in these soils is erratic and tricky, which depends upon the available P status in soils, distribution of rainfall, adsorption and desorption capacity of soil, and overall P sink created by crop depending upon its vigor. Delineation of optimum P level for higher productivity and to avoid wastage of precious P fertilizer thus becomes inevitable. Hence, an experiment was conducted at Hayathnagar Research Farm of Central Research Institute for Dryland Agriculture, Hyderabad to i) study the external (relative grain yields, agronomic efficiency, harvest index) and internal response (fertilizer P use efficiency, P uptake harvest index) indicators of sorghum to various levels of P application, ii) development of prediction functions to arrive at optimum P dose and iii) P use - removal balance for grain sorghum for these rainfed semi-arid tropical Alfisols. Results of the study indicated that P application to sorghum in these Alfisol soils beyond 23 kg ha−1 might not be much economical and desirable. It was observed that the maximum grain yield of 87% could be achieved at a leaf P concentration of 0.39% at boot leaf or flag leaf stage and 0.30% at 50% flowering stage. The prediction functions were developed to understand the quantitative relationship between external and internal response indicators. The zero P balance (neither depletion nor excessive build up) obtained at 20 kg ha−1 level (per se near 23 kg P ha−1) indicates that this level is sufficient for sorghum crop to perform with an agronomic efficiency of 19.42 kg grain kg−1 P. The findings of this study would help in efficient use of P fertilizer for achieving desirable yield levels and will in turn reduce the expenditure on P fertilizers that are mostly imported by India and majority of other developing countries.

Isolation and characterization of Ustilaginoidea virens and survey of false smut disease of rice in India

The intensity of rice false smut disease in selected states of northwest and south India was studied. In northern Indian states as a whole, disease incidence (percentage of false smut-infected tillers) varied from 2% to 75%. In the state of Haryana, maximum infection was recorded on hybrids like PA 6444 and PA 6129 while in Punjab state, 10–20% disease incidence was recorded in popular inbred rice varieties like PR 114, PA 116 and PAU 201. In the southern state of Tamil Nadu, the disease incidence varied from 5% to 85%. A heavy incidence of the disease was noticed in variety BPT 5204 and due to this, the air above the infected field gave a black smoky appearance from a distance as a result of release of spore mass in the atmosphere. In severe cases the number of infected grains reached even more than 100 per panicle. The pathogen Ustilaginoidea virens was isolated in potato dextrose agar medium and was characterized by both pathogenicity test and molecular analysis. Under glasshouse conditions, when a conidial suspension of the pathogen was injected during boot leaf stage of the rice variety TN1, typical smut balls were observed. The identity of the pathogen was further confirmed through polymerase chain reaction (PCR) analysis using U. virens-specific internal transcribed spacer (ITS) primers. The primer pair US 1-5/US3-3 and US2-5/US4-3 amplified 380 bp and 232 bp product, respectively, which are typical for the U. virens fungus.

Seed-Borne Biocontrol Agents for the Management of Rice Sheath Rot Caused by Sarocladium oryzae (Sawada) W. Gams & D. Hawksw

All the antagonist isolates obtained from rice seeds showed in vitro inhibitory effect on Sarocladium oryzae ranging from 10.90 to 82.18 per cent. Bacillus subtilis isolate 9 was found to be highly effective in inhibiting the mycelial growth of S. oryzae by 82.18 per cent. The biocontrol agents significantly reduced S. oryzae seed infection and increased seed germination and seedling vigour. Field trials conducted at four different locations indicated that the seed-borne S. oryzae in rice could be successfully managed by seed treatment followed by foliar application at boot leaf stage with B. subtilis (or) P . fluorescens .

Genetical and anatomical analyses of a leaf flecking mutant in Triticum aestivum L.

Flecking trait in the mutant C591 (M8) Triticum aestivum L. is a stable,developmentally programmed, dominant mutation under monogenic control resembling pathogenic attack and starts appearing only from boot leaf stage of the plant. Mutant plants differ significantly from normal plants in terms of total chlorphyll contents only at later stages of symptom spread when the flecks fully cover the leaf sheath and leaves. However, total grain weight per main spike of mutant did not differ significantly from the normal plants. Microscopic studies of the mutant leaves did not reveal any damaging effect of the mutation on leaf anatomy per se, even though differences were observed in chlorophyll filling in mesophyll cells. Considering the peculiar characteristics of the mutation, many of which resembling the disease lesion mimic mutations in other crops, this is suspected to be such a mutation in wheat.

PHOSPHORUS MANAGEMENT FOR LOW LAND TRANSPLANTED RICE: A TEST VERIFICATION TRIAL WITH 2% DAP SPRAY

An experiment was conducted during June 1993 to February 1994 to study the effect of phosphorus levels and 2% DAP spray on lowland rice (Oryza sativa L.). Application of P at recommended dose (38 kg P:Os/ha) with 2% DAP spray given thrice at boot leaf, 50% flowering and post-milk stages would result in higher rice grain productivity and profitability. Considering soil health and increase in P fertilizer price, the farmer may choose to apply P at 50% of recommended dose (19 kg P₂Os/ha) with 2% DAP spray twice at boot leaf stage and 50% flowering or at post milk stages if capital is constraint for the farmer. Based on the previous season result, test verification trial was conducted in the Rabi season with I.R.20 as test variety. Similar trend was also observed in the test verification trial. The effect on P uptake at different stages of crop growth and economics were also discussed.

Evaluation of genetic resistance fromOryza sativa andOryza officinalis againstCochliobolus lunatus in Tamil Nadu, India

A new sheath rot disease of rice incited byCochliobolus lunatus (anamorph:Curvularia lunata) was first observed on rice cultivars at the end of the dry season (April and May) in 1990. Nearly 7% of rice plants at boot leaf stage showed typical sheath rot symptoms. Panicles emerging from diseased plants were mostly black. Six improved cultivars and five breeding lines derived from the wild riceOryza officinalis were completely free of the disease under both natural and artificial infection conditions. These genetic stocks with resistance to sheath rot can now be utilized in breeding programs.

Analysis of ATPase and succinic dehydrogenase in F1 hybrids of rice (Oryza sativa L.)

Activities of ATPase and succinic dehydrogenase were assessed in three F1 hybrids of rice and their parental lines during boot leaf stage, flowering, on 10th and 20th days after flowering. ATPase activity showed increase at the flowering and on 20th day after flowering. Succinic dehydrogenase activity continued to rise till 10th day after flowering and declined on 20th day after flowering. Hybrids with high yield were generally endowed with more positive heterosis for these two enzymes. Correlation coefficient of grain yield per panicle was significantly positive with ATPase activity at all the stages studied. Heterosis for ATPase activity might serve a reliable criterion for the selection of efficient F1 combinations.