Irrigated cotton in the tropical dry season. III: Impact of temperature,cultivar and sowing date on fibre quality

Depending on sowing month, temperatures during boll growth in the tropical dry season are potentially sub- or supra optimal for the fibre quality parameters length and strength. The aims of this research were to: (1) measure the effect of sowing date on the quality of fibre from cotton grown during the dry season as this was not known; (2) use the range in temperature created by varying sowing date in the dry season, to derive relationships with gin turnout, the fibre quality parameters length, strength and micronaire. Over three seasons, two Gossypium hirsutum (upland) cultivars and one Gossypium barbadense cultivar were sown from March to June at the Ord River (15.5°S), Western Australia. For the highest yielding sowing months of March and April, fibre length and strength were at or below market preference due to relatively low temperatures and solar radiation during early fibre development. Fibre micronaire achieved market preference at all sowing months due to favourable late season temperatures and radiation. It is likely that current G. barbadense cultivars will have short fibre when grown in the dry season. For fibre length and gin turnout quadratic responses (p < 0.05) to weighted minimum temperature were fitted for each cultivar, where the optimum minimum temperature was 18–20 and 16–17 °C, respectively. The cultivar differences in fibre properties observed here suggest that wider screening may identify G. hirsutum cultivars with suitable fibre length and strength in the dry season. It was demonstrated by weighting of temperatures for the contribution of the cohort of bolls pollinated each day; the variation in crop fibre quality and gin turnout in the field due to temperature can be predicted.     

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.     

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/m²/day for 78–134 days compared with 15–25 g/m²/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.     

Drought conditions induce mote formation in interspecific cotton hybrids

Motes are cotton ovules that fail to ripen into mature seeds, developing instead into aborted structures which cause imperfections in ginned fibers and textile products from cotton. Interspecific hybrids (ISHs) of cotton (Gossypium hirsutum L. × G. barbadense L.) tend to produce a high number of motes. The term motes refers to various types and sizes of aborted structures which result from different disorders, may have different effect on lint quality and may be affected differently by various factors. This research was aimed at studying the effect of irrigation regime on the formation of mote of various sizes in ISHs. Five ISHs were examined in 1993 and four ISHs and two control cultivars (G. hirsutum L. and G. barbadense L.) were evaluated in 1994 in the field under both dryland and irrigated treatments. Motes found in seed-cotton samples were sorted into small, medium, and large sizes, and counted. In 1994, flowers were tagged at several stages, and the formation of motes at different reproductive phases was examined. Between 21 and 56% of the total seed potential developed into motes in the ISHs vs. 11 to 28% in the control cultivars. Moreover, when considering mote numbers per gram of fiber, which was previously found to be more closely related to nep (tangled fibers) number, total mote numbers were up sevenfold higher in the ISHs than in the control cultivars. Analyses of motes by size category revealed that numbers of small and medium motes in ISHs were higher than in controls, whereas numbers of large motes were similar. The number of small and large motes from the dryland treatment was 2 to 5 times greater than from the irrigated treatment, whereas medium motes were unaffected by irrigation. The number of small and large motes also increased under dryland conditions as the reproductive process progressed. It was concluded that drought conditions induce the formation of small and large motes, whereas medium motes result from embryo abortion due to genetic disorders.     

Analysis of cold tolerance in sorghum under controlled environment conditions

Grain sorghum (Sorghum bicolor (L.) Moench) originated in the semi-arid tropics and is generally sensitive to low-temperature stress. Early planting and use of minimum tillage necessitate the development of sorghum hybrids with early season cold tolerance. Genetic variability for cold tolerance exists in sorghum and has been detected by early planting under field conditions and by analysis of seeds and plants under growth chamber conditions. There is limited information on the efficiency of evaluating cold tolerance under growth chamber conditions and the relationship with field performance. The objectives of this study were to quantify the variability of cold tolerance in commercial hybrid seed lots under growth chamber conditions, to exam different components of cold tolerance and their relationships, and to evaluate the consistency of lab test results with data from field tests. Thirty commercial hybrid seed lots were evaluated by growing the entries under 15/10, 13/10, 11/8, and 25/20 °C day/night temperature in a 13/11 h cycle in a growth chamber. Traits measured included emergence percentage, emergence index, shoot and root dry weight, seedling height, and vigor score. Significant genotypic differences were detected for all traits. Correlations among the traits were significant and favorable, which confirmed that simultaneous improvement of these traits should be possible. The same seed lots were also evaluated in a soil-free plate-based assay, in which percent germination, and shoot and root elongation of the seed lots grown in dark at 15 °C were measured. Results from both laboratory tests, soil-based and plate-based, were correlated with data collected in a field study, which was conducted to evaluate cold tolerance of commercial sorghum hybrids at Manhattan, Hesston, Bellville, and Garden City, KS in 1998 and 1999. Single-trait correlations between lab and field studies were significant. Differentiation based on rank-summation index of common traits, rank-summation index correlations and the overlap of best entries, further provided strong support of the efficiency of predicting and identifying elite hybrids using growth chamber assays.     

Relative Fitness of Helicoverpa armigera (Lepidoptera: Noctuidae) on Seven Host Plants: A Perspective for IPM in Brazil

The cotton bollworm Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a widespread pest of many cultivated and wild plants in Europe, Africa, Asia, and Australia. In 2013, this species was reported in Brazil, attacking various host crops in the midwestern and northeastern regions of the country and is now found countrywide. Aiming to understand the effects of different host plants on the life cycle of H. armigera, we selected seven species of host plants that mature in different seasons and are commonly grown in these regions: cotton (Gossypium hirsutum, “FM993”), corn (Zea mays, “2B587”), soybean (Glycine max, “99R01”), rattlepods (Crotalaria spectabilis), millet (Pennisetum glaucum, “ADR300”), sorghum (Sorghum bicolor, “AGROMEN70G35”), and cowpea (Vigna unguiculata, “SEMPRE VERDE”). The development time of immatures, body weight, survivorship, and fecundity of H. armigera were evaluated on each host plant under laboratory conditions. The bollworms did not survive on corn, millet, or sorghum and showed very low survival rates on rattlepods. Survival rates were highest on soybean, followed by cotton and cowpea. The values for relative fitness found on soybean, cotton, cowpea, and rattlepods were 1, 0.5, 0.43, and 0.03, respectively. Survivorship, faster development time, and fecundity on soybean, cotton, and cowpea were positively correlated. Larger pupae and greater fecundity were found on soybean and cotton. The results indicated that soybean, cotton, and cowpea are the most suitable plants to support the reproduction of H. armigera in the field.     

The use of bacterial antagonists for the control of cotton diseases

Three antagonistic bacteria, Pseudomonas fluorescens 41, Bacillus subtilis 23 and Bacillus megatherium 26, were tested for their ability to control agents of major cotton diseases Xanthomonas malvacearum, Rhizoctonia solani, Fusarium vasinfectum and Verticillium dahliae. Control was achieved in several trials and results demonstrated that the antagonism of tested isolates was in some versions active and in others passive. In laboratory experiments, Bacillus subtilis 23 was the most effective against three of the four phytopathogenic microorganisms. In field trials, the influence of antagonists' metabolites on seed germination, early seedling development, yield of Upland varieties of cotton Gossipium hirsutum 108-F and Kirgiziya-3 and on infection with X. malvacearum and R. solani, were studied. Cultural liquids of all tested antagonists in a dilution 1:9 suppressed development of phytopathogens, and had a stimulating effect on emergence of seedlings, their early growth and cotton yield, and inhibited development of diseases. In this case the most effective antagonists were B. subtilis 23 and P. fluorescens 41.     

Effects of fungicide seed treatments on germination, population, and yield of maize grown from seed infected with fungal pathogens

Seedborne fungi can reduce survival, growth, and yield of maize (Zea mays L.). Laboratory, field, and growth chamber experiments were conducted to determine the effects of the seed treatment fungicides fludioxonil, mefenoxam, and azoxystrobin on germination, plant population, and grain yield of maize grown from low-quality hybrid seed infected with seedborne fungal pathogens. Study I used seed of four hybrids infected at 0-54% incidence with Fusarium spp., Stenocarpella maydis, Penicillium spp., Rhizopus spp., and/or Aspergillus spp. Study II used three seed lots for each of two hybrids infected at 7-37% incidence with S. maydis. Warm and cold germination for untreated seed varied among hybrids in both studies. Warm germination of the seed lot with the highest incidence of S. maydis in study II treated with azoxystrobin and fludioxonil was significantly greater (+7%) than the nontreated control. Plant population in study I was significantly affected by seed treatment, hybrid, and their interactions. Populations were greater (≥9%) for fludioxonil, fludioxonil + mefenoxam, and fludioxonil + mefenoxam + azoxystrobin treatments compared to controls. In growth chamber experiments with pasteurized soil, emergence (≥5%) and plant dry weight (≥14%) were both greater than controls only with the triple seed treatment. Plant populations in study II for all seed treatments except mefenoxam and azoxystrobin alone were greater (≥4%) than controls. Yield in study I was significantly affected by hybrid and seed treatment. Yield for one hybrid was higher (≥20%) than the control with all seed treatments except fludioxonil, whereas yield with another hybrid was consistently greater (≥26%) only with the triple seed treatment. Yield in study II was significantly affected by hybrid, seed treatment, and their interactions. Yield was greater (≥8%) than the controls for all seed treatments with one hybrid and with all (≥5%) except azoxystrobin for the other hybrid. Highest yields occurred with the triple seed treatment. Results indicate that fludioxonil and azoxystrobin can increase germination, population, and yield of maize grown from seed infected by S. maydis and other fungi.     

Variability in germination behaviour of Paspalum dilatatum Poir. seeds is genotype dependent

Dallisgrass (Paspalum dilatatum Poir.) is a warm‐season grass, native to South America. Its adoption as a pasture crop has been hindered by low seed germination and slow establishment. However, variability in germination behaviour for this species has never been systematically analysed. For Paspalum spp., dry‐storage and moist cold or warm pre‐conditioning treatments have been reported as effective for the relief or breaking of seed dormancy. In the present work, seed germination responses at 32°C were assayed for sixteen P. dilatatum genotypes, representing its known natural genetic variability, to two moist pre‐conditioning treatments (at 5 and 20°C) and without pre‐conditioning, and three seed storage periods (0, 3 and 6 months). Pre‐conditioning at 20°C showed high germination percentages (>80%), with ratios equal to or higher than pre‐conditioning at 5°C, suggesting that cold is not required to break dormancy. Longer storage times resulted in increases in germination responses for most of the genotypes, while other biotypes showed no effect. Biotypes Virasoro and Chirú showed a remarkably different behaviour with higher germination percentages of untreated freshly harvested seeds. Our results show that diversity for traits involved in seed germination exists among naturally occurring P. dilatatum genotypes and the characterization of these traits should be addressed during ecotype characterization and evaluation of potential domesticates of this species.     

Manual topping decreases bollworm infestations in cotton cultivation in Mali

In sub-Saharan areas of Africa, cotton growers no longer cut the shoot tips from plants (topping), although manual topping was promoted at the start of the 20th century to improve yield and, surprisingly, to reduce pest incidence. In these areas, the bollworms Helicoverpa armigera Hübner, Earias spp., and Diparopsis watersi Rothschild are responsible for the majority of cotton yield losses, and the use of pyrethroids has resulted in resistance in field populations of H. armigera. In the face of these problems and given the scarcity of literature on the effects of topping on pest control, we assessed bollworm infestation levels in 12 trials comparing manual topping and non-topping cotton plots in Mali over a six-year period (2002, 2003, and 2005 to 2008). Topping was performed at the emergence of the 15th sympodial branch or at 10 days after the first flower opening. Our results showed no significant difference in seed cotton yields between topped and non-topped cotton. Bollworm infestations (all species) were always lower on topped cotton and 7 out of 12 trials showed significantly lower infestations on topped cotton. In plots of topped cotton, we recorded an average of 56% fewer H. armigera larvae, 68% fewer Earias spp. larvae, and 71% fewer D. watersi larvae with respectively 5, 4, and 3 out of 12 trials with significant differences in favor of topping and no significant difference in favor of non-topping. To our knowledge, our study is the first to report decreases in D. watersi larval infestation with cotton topping. Further studies are required to understand the mechanisms involved in these effects and to ensure that topping is economically attractive for farmers.     

Thermal tolerance of propagative anthurium stem cuttings to disinfestation by heat treatment for burrowing nematodes and bacterial blight

Hot water and hot air treatments were evaluated for disinfesting anthurium, Anthurium andraeanum Lind., stem cuttings of the bacterial blight pathogen, Xanthomonas axonopodis pathovar dieffenbachiae (Xa pv. dieffenbachiae), and burrowing nematodes, Radopholus similis, and their effect on viability of the cuttings. Xa pv. dieffenbachiae suspended in distilled water in 1.5 ml microcentrifuge tubes, lost at least 6 logs of viability when exposed to hot water at 50 °C for 12 min or hot air at 50 °C, 60% RH for 35 min administered in commercial-sized heat treatment facilities. Stem cuttings exposed to hot air at 50 °C, 60% RH were disinfested of R. similis when their core temperatures attained 50 °C. Plant response to heat treatments varied among cultivars; however, all evaluated cultivars exhibited high tolerance to hot water at 50 °C for up to 24 min with equal or enhanced sprouting rates as compared to untreated checks. Sprouting rates of three of the four cultivars treated with hot air at 50 °C, 60% RH for up to 125 min were equal to or higher than untreated checks, while cuttings from the less tolerant cultivar ‘Tropic Fire’ registered lower sprouting rates for all hot air treatment durations as compared to untreated checks, Flower quality parameters, including average spathe size, stem diameter and number of flowers harvested from plants heat-treated as cuttings, were comparable to or higher than untreated checks for all treatments and cultivars. Disinfestation of anthurium stem cuttings for bacterial blight and the burrowing nematode can be achieved in hot water at 50 °C for 24 min without loss of sprouting rate or flower quality.     

Ecological studies on Echinochloa crus-galli and the implications for weed management in direct-seeded rice

Echinochloa crus-galli, a C₄ grass, is one of the world’s most serious weeds. Weed management decisions for this species can be derived from knowledge of its seed biology. Studies were conducted to determine the effects of light on germination; seed burial depth and rice residue on emergence and growth; and flooding time and depth on emergence, survival and growth of this species. Light stimulated seed germination but it was not an absolute requirement for germination. The proportion of seeds germinating was greatest for seeds placed on the soil surface (92%), and emergence declined with increasing burial depth in soil; no seedlings emerged from the depth of 8 cm. A burial depth of only 0.4 cm reduced seedling emergence by 50%. Seedling emergence and seedling biomass were reduced by the addition of high level (6 ton ha⁻¹) of rice residue to the soil surface. Early and deep flooding significantly suppressed growth of E. crus-galli seedlings. In flooded conditions, with increased water depth the weed allocated more biomass to shoots at the expense of roots. The information gained from this study could contribute to improve weed control approaches. Soil inversion by tillage to bury weed seeds below their maximum depth of emergence, use of crop residue as mulch and early flooding of the crop could serve as important tools for managing E. crus-galli and other weed species with similar germination requirements. These management options, however, would need to be compatible with other crop management requirements.     

Frequency of Bt resistance alleles in Helicoverpa armigera in 2007-2009 in the Henan cotton growing region of China

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a key insect pest of cotton in the Henan cotton growing region of China. In this region, cotton is grown on small acreages in rich agricultural landscapes, contrary to cropping systems in the United States or Australia. Under such cropping regimes, naturally occurring refuges (with non-Bt plants) may be sufficient to prevent H. armigera resistance development to Bt toxins. In order to gain a timely understanding of the evolution of resistance of H. armigera to Bt toxin after continuous cultivation of Bt cotton for c. 10 years, we assessed the frequency of alleles conferring resistance to Cry1Ac toxin in field populations of H. armigera sampled from Xinxiang County in Henan province during 2007-2009. Screening F₁ and F₂ generations from isofemale lines, derived from female moths trapped in the field, were used with a discriminating dose of Cry1Ac diet to estimate the frequency of resistance alleles. Totals of 625, 516 and 488 isofemale lines were screened for the F₁ generation in 2007, 2008 and 2009, respectively. Resistance gene frequency in Xinxiang fluctuated between 0.0000 and 0.0005, and it did not increase significantly from 2007 to 2009. Based on the relative average development rates (RADR) of H. armigera larvae in F₁ tests, no substantial increase in Cry1Ac tolerance was found in the Xinxiang region over the 3-yr period.     

Kenaf seed storage duration on germination,emergence, and yield

Kenaf (Hibiscus cannabinus L.) is a potential alternative crop being developed for fiber production. Because planting area varies dramatically from year to year, seed supplies may greatly exceed use so that the excess seed must be stored for one to several years. The objectives of this study were to determine the effect of seed storage duration at 10 °C on germination, vigor, emergence, and yield. Replicated trials were established at Starkville, MS in 1999 and 2000 to evaluate field emergence and biomass yield of kenaf seed from five ‘Everglades 41’ (‘E41’) harvest year seed lots stored at 10 °C in ambient relative humidity for up to 4 years. Germination of these same seed lots under standard (20–30 °C) and cool (20 °C) temperatures, and seed vigor was evaluated over time. Field emergence was the same for the different seed storage durations up to 4 years, but was directly affected by drought conditions for each planted year. Biomass yields ranged from 12.39 to 14.57 Mg ha⁻¹ in 1999 and 16.82 to 18.47 Mg ha⁻¹ in 2000, but were not different between storage durations. Seed germination remained greater than 80% regardless of storage duration. Electrolyte leakage, based on conductivity, was 38–50% less with freshly harvested seed than seed stored for 4 years at 10 °C. However, neither the conductivity nor accelerated aging test were reliable predictors of field emergence. Kenaf seed stored up to 4 years at 10 °C retained germination rates acceptable for commercial use. Neither field emergence nor biomass yield was affected by seed storage duration.     

The influence of rainfed and limited irrigation conditions and early vs. late plantings on kenaf as a potential industrial crop in the southern High Plains,USA

Kenaf (Hibiscus cannabinus L.) is a nonwoody fiber source with many uses. To evaluate the dry matter yield potential of kenaf at two locations in the southern High Plains of the USA and the effects of late planting/late emergence as a possible replacement for hail damaged cotton, four varieties were grown in 2004 and 2005 at New Mexico State University's Agricultural Science Centers at Clovis, under limited irrigation, and Tucumcari, under rainfed conditions. Each study was a randomized complete block design having four replicates. A year × location interaction existed (P < 0.0469) for kenaf yield largely due to precipitation amount and distribution. Either late planting or late emergence due to low soil moisture at planting significantly reduced yields (3.62 vs. 0.63 Mg ha^?1 for mid-May planting and emergence and early July emergence or planting, respectively, P < 0.0001). Consequently, kenaf would not be suitable for recovering input costs when planted after failure of cotton. The very late maturing variety Gregg had consistently lower numeric yields than Dowling, Everglades 41, and Tainung 2 in all comparisons, with the strongest trend within the emergence date comparison (P < 0.0912). Kenaf varieties should be selected for any location that finish blooming approximately three to four weeks prior to the average first autumn freeze to allow for maximum growth.     

Effects of after-ripening and storage regimens on seed-germination behavior of seven species of Physaria

The after-ripening response has been well documented in many plant species but studies of this topic are lacking in many new oilseed crops such as Physaria. In a factorial experiment, we tested the effect of different after-ripening periods and germination conditions on freshly harvested seeds of seven Physaria species, Physaria argyraea, Physaria fendleri, Physaria gracilis, Physaria rectipes, Physaria recurvata, Physaria sessilis, and Physaria thamnophila. The seeds were stored for 4 and 12 weeks over two saturated salt solutions (LiCl and MgCl₂) to equilibrate seed moisture at three storage temperatures (5, 25, and 35 °C). We likewise tested a dormancy-breaking protocol on these species by using conditions previously recommended for use in genebanks for P. fendleri. The germination tests were conducted with light (1052 lux) and gibberellic acid (GA₃) (100 ppm) and without them. Results suggested that conditions previously set for P. fendleri are also adequate for P. gracilis, P. recurvata, and P. sessilis, but may still be not optimal for the perennial species, P. argyraea, P. thamnophila, and P. rectipes. Overall, higher germination percentages were obtained with light and GA₃ treatments. In all species, we observed slight differences between total germination results after 4 weeks and 12 weeks of storage, with higher values evident only in P. fendleri, P. recurvata, and P. thamnophila after their fresh seeds were subjected to 12 weeks of after-ripening at warm temperatures.     

Factors affecting sporulation of Pestalotiopsis disseminata causing grey blight disease of Persea bombycina Kost., the primary food plant of muga silkworm

The effect of inoculum concentrations, temperature, relative humidity (RH), incubation period and leaf age on sporulation of Pestalotiopsis disseminata and the development of grey blight disease on som (Persea bombycina Kost.) were studied in controlled environmental conditions. These factors had a significant role on spore germination and germ tube development of P. disseminata, the causal organism of the disease. The optimum inoculum concentration of the pathogen were found to be 1 × 10⁷ spores ml⁻¹ for maximum infection percentage. A nonlinear relationship was found between temperature and germination percentage of spores at a given relative humidity (RH). However, 25 °C (±2) temperature and 70% RH were the optimum parameters for better spore germination of the pathogen. Young leaves (leaf no. 1–4 from the top) were more susceptible for development of the diseases in a controlled environment than the older leaves. The germination of spores started at 8 h of incubation and gradually increased up to 20 h (maximum). The disease severity was favoured in the optimum range of temperature (25 ± 2 °C) and RH (70%) which had a combined effect. These epidemiological parameters could help in the management practices of the disease.     

Introgression of resistance to reniform nematode (Rotylenchulus reniformis) into upland cotton (Gossypium hirsutum) from Gossypium arboreum and a G. hirsutum/Gossypium aridum bridging line

Gossypium hirsutum L. is the predominant cotton of commerce and all cultivars of this species are susceptible to the reniform nematode, Rotylenchulus reniformis. To introgress resistance to R. reniformis into the tetraploid 2(AD₁) G. hirsutum, a resistant diploid A₂-genome Gossypium arboreum accession (A₂-190) was crossed with a hexaploid 2((AD₁)D₄) bridging line (G 371) to obtain a tetraploid triple-species hybrid. The triple-species hybrid was back-crossed to G. hirsutum and a population of 277 BC₁ individuals was produced. The BC₁s and controls were assayed in growth chambers for resistance to R. reniformis. Fortuitously, the hexaploid bridging line G 371 was also found to be resistant to R. reniformis. The BC₁ segregated 3:1, resistant:susceptible, indicating that resistance was conferred by dominant genes at two different loci, with each originating from a distinct germplasm source. This study demonstrated that it is possible to introgress and pyramid genes for resistance to R. reniformis in G. hirsutum.     

Overwintering hosts of Apolygus lucorum (Hemiptera: Miridae) in northern China

During the past decade, Apolygus lucorum Meyer-Dür (Heteroptera: Miridae) has become a key pest of cotton in northern China, due to widespread planting of Bt cotton and an associated drop in the use of broad-spectrum insecticides. Because of a lack of management alternatives, A. lucorum outbreaks are presently exclusively controlled with insecticides. In this study, we determined A. lucorum overwintering locations and host plants during the 2006–2009 winter seasons. A total of 126 plant species were screened and nymphal emergence of A. lucorum was monitored over time. Eggs of A. lucorum successfully overwintered in cotton field soils and on 86 plant species, including weeds, fruit trees, pastures and agricultural crops. More specifically, Vitis vinifera L., Ricinus communis L., Momordica charantia L., Artemisia argyi Levl. et Vant., Artemisia annua L., Artemisia lavandulaefolia DC., Isatis indigotica Fort., Artemisia scoparia Waldst. et Kit., Vigna radiate (L.) Wilczek, Ziziphus jujuba Mill., Vigna angularis (Willd.) Ohwi et, Ocimum basilicum L., Onobrychi viciifolia Scop., Pyrus bretschneideri Rehd., Malus domestica Borkh. and Brassica juncea (L.) Czern. et Coss proved optimal overwintering hosts of A. lucorum. Based upon plant species occurrence and distribution in Chinese cotton-growing regions, several weeds and fruit trees, such as V. vinifera, Z. jujuba, P. bretschneideri and M. domestica can be termed key overwintering hosts of A. lucorum. Our findings can form the basis for future formulation of targeted management actions to lower A. lucorum overwintering populations in cotton-growing landscapes of northern China.     

Cropping calendar options for rice-wheat production systems at high-altitudes

The onset of rains during dry to wet transition fallow periods in rice-wheat production systems in Nepal cause substantial losses of soil nitrogen if the system is improperly managed. To make use of available nutrients and water, this transition period can either be shortened by early rice planting, or be extended by late planting, allowing a third crop to be grown. Shifting planting dates would require rice genotypes adapted to the different environments. Crop duration is influenced by both vegetative and reproductive development, which in turn is influenced by the photo-thermal environment and genotypic responses to it. An experiment was conducted to derive genotypic photo-thermal constants from phenological observations on diverse rice cultivars, which were then applied to the concept of the phenological model RIDEV to design cropping calendar options. Environmental effects on variation of crop duration were determined by planting at different dates. The risk of yield losses to sterility caused by low temperatures was estimated by simulation. Thirty-one different genotypes of rice were planted at 8 dates in 15-day intervals starting 27 April 2004 at the experimental field of the Regional Agriculture Research Station, Lumle, Nepal. The shortest duration to flowering was observed for planting dates in late May and early June. Simulation of flowering dates with RIDEV yielded correct results only for the early planting dates. For later planting dates simulated flowering dates showed an increasing deviation from the observed. In most cultivars, minimum air temperature below 18 °C during booting to heading stages caused near-total spikelet sterility and a specific delay in flowering. However, the chilling tolerant cultivars Chomrong and Machhapuchre-3 cultivated at high altitude showed less than 30% spikelet sterility even at 15 °C. Simulating crop durations with the derived thermal constants allowed evaluating the different calendar options for high altitude systems.