Seed longevity of maize conserved under germplasm bank conditions for up to 60 years

Background and AimsThe long-term conservation of seeds of plant genetic resources is of key importance for food security and preservation of agrobiodiversity. Nevertheless, there is scarce information available about seed longevity of many crops under germplasm bank conditions.MethodsThrough germination experiments as well as the analysis of historical monitoring data, we studied the decline in viability manifested by 1000 maize (Zea mays subsp. mays) seed accessions conserved for an average of 48 years at the CIMMYT germplasm bank, the largest maize seedbank in the world, under two cold storage conditions: an active (–3 °C; intended for seed distribution) and a base conservation chamber (–15 °C; for long-term conservation).Key ResultsSeed lots stored in the active chamber had a significantly lower and more variable seed germination, averaging 81.4 %, as compared with the seed lots conserved in the base chamber, averaging 92.1 %. The average seed viability detected in this study was higher in comparison with that found in other seed longevity studies on maize conserved under similar conditions. A significant difference was detected in seed germination and longevity estimates (e.g. p₈₅ and p₅₀) among accessions. Correlating seed longevity with seed traits and passport data, grain type showed the strongest correlation, with flint varieties being longer lived than floury and dent types.ConclusionsThe more rapid loss of seed viability detected in the active chamber suggests that the seed conservation approach, based on the storage of the same seed accessions in two chambers with different temperatures, might be counterproductive for overall long-term conservation and that base conditions should be applied in both. The significant differences detected in seed longevity among accessions underscores that different viability monitoring and regeneration intervals should be applied to groups of accessions showing different longevity profiles.     

Effects of elevated CO2 on plant growth and nutrient partitioning of rice (Oryza sativa L.) at rapid tillering and physiological maturity

Abstract

This work investigates the relationship between plant growth, grain yield, nutrient acquisition and partitioning in rice (Oryza sativa L.) under elevated CO₂. Plants were grown hydroponically in growth chambers with a 12-h photoperiod at either 370 or 700 µmol CO₂ mol^?1 concentration. Plant dry mass (DM), grain yield and macro- and micronutrient concentrations of vegetative organs and grains were determined. Elevated CO₂ increased biomass at tillering, and this was largely due to an increase in root mass by 160%. Elevated CO₂ had no effect on total nutrient uptake (N, P, K, Mg and Ca). However, nutrient partitioning among organs was significantly altered. N partitioning to leaf blades was significantly decreased, whereas the N partitioning into the leaf sheaths and roots was increased. Nutrient use efficiency of N, P, K, and Mg in all organs was significantly increased at elevated CO₂. At harvest maturity, grain yield was increased by 27% at elevated CO₂ while grain (protein) concentration was decreased by a similar magnitude (28%), suggesting that critical nutrient requirements for rice might need to be reassessed with global climate change.     

Winter use of wild bird cover crops by passerines on farmland in northeast England

Capsule Declining farmland species were more abundant in these crops which can be matched to the birds' requirements.

Aims To assess the use of seed-bearing crop by a range of bird species in winter.

Methods The study was carried out over three winters at a site in County Durham (England). Eleven bird species were represented, five of which are nationally targeted for conservation action.

Results Bird abundance was significantly higher where wild bird cover crops were present. Kale Brassica napus and Quinoa Chenopodium quinoa were the most used crop species, although cereals and linseed were also used.

Conclusion Simple crop mixtures can be designed to meet the needs of farmland bird communities. Our results suggest that seed production may be limited within government agri-environment schemes by restrictions on fertilizer use. The agronomy of seed-bearing crops for birds requires further investigation.     

Spatial and temporal variation in the control failure likelihood of the tomato leaf miner,Tuta absoluta

Insecticide resistance is frequently associated with field control failure, but such an assessment of its likelihood seldom occurs. This phenomenon is a potential cause of the control failure of the tomato leaf miner Tuta absoluta (Lepidoptera: Gelechiidae); therefore we surveyed insecticide resistance as the control failure likelihood for a duration of 7 years in 20 field populations of this species. The insecticide label rate was used as the discriminating concentration, and the minimum efficacy threshold required for insecticides in Brazil (i.e. 80% efficacy) was the targeted efficacy. The spatial and temporal variations of the control failure likelihood were also assessed, as was the potential influence of land topography for the area‐wide pattern observed. Most populations of T. absoluta were susceptible to abamectin, chlorfenapyr and spinosad and not to bifenthrin, triflumuron and teflubenzuron. The indoxacarb susceptibility varied in space and time. Spatial dependence was observed for abamectin and indoxacarb. The control failure likelihood of T. absoluta was higher for bifenthrin, triflumuron and teflubenzuron. A flat topography and the wind direction may favour the spread of the control failure likelihood and should be considered in designing pest management programs for T. absoluta.     

Efficiency of food utilization by Dichroplus maculipennis (Orthoptera: Acrididae: Melanoplinae) on four crop plants under controlled conditions

The aim of this study was to analyze the food utilization efficiencies and the relative growth and consumption rates of different developmental stages and sexes of D. maculipennis under controlled conditions on wheat, oat, corn, and soybean plants, important crops in the Pampas region of Argentina. As expected from a polyphagous species, D. maculipennis was observed to consume all four of the plant species offered. Nevertheless, the consumption of both nymphs and adults was differentiated. Oat and wheat were more consumed than corn and soybean. Females presented higher consumption rates (384.6 ± 30.64 mg/individual/day) than males (278.71 ± 24.26 mg/individual/day). Adult females had the highest growth rate, followed by nymphs of the same sex, and then adult males. The highest values of ECI and ECD were obtained in soybean; females had higher values of food efficiencies than males, and nymphs had greater values than adults. In relation to this, soybean was the highest quality food; the amount of nitrogen present in soybean was approximately twice that found in the other species. The nutritional needs of D. maculipennis might have been satisfied by feeding on low quantities of soybean, which is, among the food offered, the most “nutritionally balanced food”.     

Dissimilarity of contemporary and historical gene flow in a wild carrot (Daucus carota) metapopulation under contrasting levels of human disturbance: implications for risk assessment and management of transgene introgression

Background and Aims

Transgene introgression from crops into wild relatives may increase the resistance of wild plants to herbicides, insects, etc. The chance of transgene introgression depends not only on the rate of hybridization and the establishment of hybrids in local wild populations, but also on the metapopulation dynamics of the wild relative. The aim of the study was to estimate gene flow in a metapopulation for assessing and managing the risks of transgene introgression.

Methods

Wild carrots (Daucus carota) were sampled from 12 patches in a metapopulation. Eleven microsatellites were used to genotype wild carrots. Genetic structure was estimated based on the F_ST statistic. Contemporary (over the last several generations) and historical (over many generations) gene flow was estimated with assignment and coalescent methods, respectively.

Key Results

The genetic structure in the wild carrot metapopulation was moderate (F_ST = 0·082) and most of the genetic variation resided within patches. A pattern of isolation by distance was detected, suggesting that most of the gene flow occurred between neighbouring patches (≤1 km). The mean contemporary gene flow was 5 times higher than the historical estimate, and the correlation between them was very low. Moreover, the contemporary gene flow in roadsides was twice that in a nature reserve, and the correlation between contemporary and historical estimates was much higher in the nature reserve. Mowing of roadsides may contribute to the increase in contemporary gene flow. Simulations demonstrated that the higher contemporary gene flow could accelerate the process of transgene introgression in the metapopulation.

Conclusions

Human disturbance such as mowing may alter gene flow patterns in wild populations, affecting the metapopulation dynamics of wild plants and the processes of transgene introgression in the metapopulation. The risk assessment and management of transgene introgression and the control of weeds need to take metapopulation dynamics into consideration.     

Weed and crop plants as reservoirs of peanut bud necrosis tospovirus and its occurrence in South India

Survey was carried out on occurrence of peanut bud necrosis disease (PBND) in Karnataka and Andhra Pradesh (AP) the major groundnut growing states in South India. PBND incidence was observed on crops, viz., greengram, blackgram, tomato, watermelon, cowpea, chilli, cucumber and sesame besides groundnut. The PBND incidence was higher in rainy season crops than in post-rainy season. Its proportion varied from place to place, and it was high in the vegetable and pulses growing areas. The weed plant species Achyranthus aspera, Acalypha indica, Alysicarpus rugosus, A. longifolia, Commelina bengalensis, Commelina jacobi, Corchorus trilocularis, Cyanoptis cuculetta, Eclipta alba, Euphorbia geniculata, Lochnera pusilla, Physalis minima and Sesbania rostrata were recorded for the first time as alternate hosts of PBND. Infection was also noticed for the first time on cucumber, muskmelon and sesame crops. Five weed species, viz., Achyranthus aspera, Ageratum conyzoides, Alysicarpus rugosus, Commelina bengalensis and Vigna trilobata were found abundant in AP and Karnataka. More infection was observed on Ageratum conyzoides (17.56%) compared with other weeds.     

Parasitoids as a bioagent to eliminate the insecticides to control the main pests-infested economic crops

Hemipterous insects are one of the important pests that attack different economic plants. A study was conducted to evaluate the biological control potential of these pests by augmentation with parasitoids, such as Microterys flavus (Howard), Metaphycus lounsburyi Howard (Encyrtidae), Encarsia sophia (Girault and Dodd), Coccophagus scutellaris (Dalman), Aphytis melinus DeBach (Aphelinidae) and Aphidius ervi Haliday (Braconidae). All the species were mass reared and monthly releases were made in fields of citrus, olive, tomato, sugar cane, mango and squash during each of 11 consecutive years (1999–2009). About 5,830,000 individuals of M. flavus, M. lounsburyi, E. sophia, C. scutellaris, A. melinus and A. ervi were released in the fields of Gharbiya, Marsa Matrouh, Daqahlyia, Qena, Qalyubiya and Behira governorates in Egypt on citrus, olive, tomato, sugar cane, mango and squash which were naturally infested by Ceroplastes floridensis Comstock, Saissetia oleae (Olivier) (Coccidae), Bemisia tabaci (Gennadius) biotype Q (Aleyrodidae), Pulvinaria tenuivalvata (Newstead) (Coccidae), Aulacaspis tubercularis (Newstead) (Diaspididae) and Aphis craccivora Koch (Aphididae), respectively. Population of the parasitoids and parasitism increased in field plots where releases were made when compared with where no releases were made. The maximum rate of parasitism reached 61.4, 92.1, 45.7, 59, 91 and 55.2% in the field treatment where releases were made, while parasitism peaked at 8.2, 13.5, 6, 2, 16 and 17.5% where no releases were made. The populations of M. flavus, M. lounsburyi, E. sophia, C. scutellaris, A. melinus, A. ervi were significantly correlated with the populations of C. floridensis, S. oleae, B. tabaci, P. tenuivalvata, A. tubercularis and A. craccivora during the field seasons. Additional parasitism was caused by natural infestations of Metaphycus helvolus (Compere) and M. lounsburyi (Howard) (C. floridensis), Scutellista cyanea (Motschulsky) (S. oleae), Encarsia lutea (Masi) and Eretmocerus mundus (Mercet) (B. tabaci biotype Q), Encarsia citrina (Craw) (A. tubercularis) and Aphelinus demyaati Abd-Rabou (A. craccivora). These observations enhance the understanding of the usefulness of these parasitoids after augmentation in the field.     

Effect of cultural methods on Striga (Striga hermonthica (Del.)) Benth management and yield of cereals in the Savanna Zone of Nigeria: a review

Data were obtained from the research done in the Guinea Savanna (Zaria 11°11′N; 070 38′E) and Sudan Savanna (Maiduguri ?11°51′N; 13°15′E) regions of Nigeria, respectively on different cultural methods of Striga control and management. In the Guinea Savanna, trials on the effects of nitrogen on the response of resistant and susceptible upland rice varieties to Striga hermonthica infestation and the effect of resistant and susceptible varieties of maize and crop rotation on Striga infestation was carried out, while the effect of inter-cropping trap crop (Bambaranut) with resistant sorghum varieties on S. hermonthica was studied in the Sudan Savanna Zone of Nigeria. In the Guinea Savanna, it was observed that a combination of upland rice variety, Faro 40 and an application of 90 kg N/ha in the wet season and WAB 56-50 upland rice variety and 120 kg N/ha in the dry season, respectively reduced Striga infestation and produced maximum grain yield. Also, the growing of resistant variety of maize (Across 97ITZ comp. I-W) after 1 or 2 years' rotation with cowpea or soybean was observed not only to be effective in Striga control, but resulted in higher grain yield of maize. In the Sudan Savanna, the use of resistant varieties of sorghum, 1CSV1002 and 1CSV1007 intercropped with bambaranut significantly reduced Striga infestation, but the grain yield of the resistant varieties was low. From these studies, Faro 40 with 90 kg N/ha application rate and WAB56–50 with 120 kg N/ha were suitable for the management of Striga and for higher grain yield of upland rice in both wet and dry seasons, respectively, while Across 97ITZ comp. I-W, resistant maize variety and 1 or 2 years rotation with cowpea or soybean were also the best for the management of S. hermonthica and for higher maize yield in the Guinea Savanna zone. Further research needs to be carried out in the Sudan Savanna to select a high yielding resistant variety of sorghum which when intercropped with bambaranut will not only control Striga infestation but will also give high grain yield.