Significant Yield Penalty Research Articles

Absence of detectable yield penalty associated with insensitivity to Pleosporales necrotrophic effectors in wheat grown in the West Australian wheat belt

Genetic disease resistance is widely assumed, and occasionally proven, to cause host yield or fitness penalties due to inappropriate activation of defence response mechanisms or diversion of resources to surplus preformed defences. The study of resistance gene trade‐offs has so far been restricted to biotrophic pathogens. In some Pleosporales necrotrophic interactions, quantitative resistance is positively associated with insensitivity to effectors. Host lines that differ in sensitivity can easily be identified amongst current cultivars and advanced breeding lines. Large wheat cultivar trials were used to test whether lines sensitive or insensitive to three necrotrophic effectors from Pyrenophora tritici‐repentis and Parastagonospora nodorum differed in yield when subjected to natural disease and stress pressures in the West Australian wheat belt. There was no significant yield penalty associated with insensitivity to the fungal effectors ToxA, SnTox1 and SnTox3. Some yield gains were associated with insensitivity and some of these gains could be attributed to increased disease resistance. It is concluded that insensitivity to these effectors does not render such plants more vulnerable to any relevant biotic or abiotic stress present in these trials. These results suggest that the elimination of sensitivity alleles for necrotrophic effectors is a safe and facile strategy for improving disease resistance whilst maintaining or improving other desirable traits.

Benefits of oxygation of subsurface drip-irrigation water for cotton in a Vertosol

Australian cotton (Gossypium hirsutum L.) is predominantly grown on heavy clay soils (Vertosols). Cotton grown on Vertosols often experiences episodes of low oxygen concentration in the root-zone, particularly after irrigation events. In subsurface drip-irrigation (SDI), cotton receives frequent irrigation and sustained wetting fronts are developed in the rhizosphere. This can lead to poor soil diffusion of oxygen, causing temporal and spatial hypoxia. As cotton is sensitive to waterlogging, exposure to this condition can result in a significant yield penalty. Use of aerated water for drip irrigation (‘oxygation’) can ameliorate hypoxia in the wetting front and, therefore, overcome the negative effects of poor soil aeration. The efficacy of oxygation, delivered via SDI to broadacre cotton, was evaluated over seven seasons (2005–06 to 2012–13). Oxygation of irrigation water by Mazzei air-injector produced significantly (P < 0.001) higher yields (200.3 v. 182.7 g m–2) and water-use efficiencies. Averaged over seven years, the yield and gross production water-use index of oxygated cotton exceeded that of the control by 10% and 7%, respectively. The improvements in yields and water-use efficiency in response to oxygation could be ascribed to greater root development and increased light interception by the crop canopies, contributing to enhanced crop physiological performance by ameliorating exposure to hypoxia. Oxygation of SDI contributed to improvements in both yields and water-use efficiency, which may contribute to greater economic feasibility of SDI for broadacre cotton production in Vertosols.

Effect of 3B, 5A and 3A QTL for Fusarium head blight resistance on agronomic and quality performance of Canadian winter wheat

AbstractThe objectives of this study were to investigate (i) the correlations between Fusarium head blight (FHB) index, deoxynivalenol (DON) accumulation and percentage of Fusarium‐damaged kernels (FDK) with agronomic and quality traits and (ii) the effect associated with the presence of single QTLs for FHB resistance on agronomic and quality traits in winter wheat. The population was derived from the cross between ‘RCATL33' (FHB resistance derived from ‘Sumai 3’ and ‘Frontana’) and ‘RC Strategy’. Parental lines and recombinant inbred lines (RILs) were genotyped with SSR markers associated with the 3B, 5A and 3A QTLs. The population was planted in FHB‐inoculated nurseries and in agronomy trials. Lines in the 3B QTL class had the lowest FHB index, DON content and FDK level and did not have a significantly lower yield, thousand kernel weight or protein content compared with the lines grouped in other QTL classes (including no QTL class). Marker‐assisted selection of the 3B QTL for FHB resistance into high‐yielding FHB‐susceptible winter wheat is the recommended approach for the development of lines with increased FHB resistance without significant yield and quality penalties.

Farm-level economic impact of no-till farming in the Fort Cobb Reservoir Watershed

No-till farming has been identified as an important conservation practice with potential to improve soil quality and protect water quality. However, adoption of new tillage and production practices is determined by numerous economic and noneconomic factors in addition to land stewardship. The objective of this study was to assess the effects of fuel costs and crop yield on farm-level economics in no-till systems in comparison with other tillage systems for wheat production in southwestern Oklahoma. The Farm-level Economic Model, an annual economic simulation model, was used in conjunction with survey data from the Fort Cobb Reservoir Watershed in southwestern Oklahoma to determine impacts of alternative tillage practices on farm profits. Sensitivity analysis was performed using plausible ranges in diesel prices, winter wheat grain yields, herbicide costs, labor wages, and farm size. The results indicate that if winter wheat grain yields are not significantly impacted by tillage systems, no-till would be more profitable than conventional tillage or the current mix of tillage practices in the watershed. Only when there is a significant wheat yield penalty associated with no-till (10% or greater) might no-till be less profitable than conventional tillage or the status quo at reasonably high fuel prices. In general, for each 1% improvement in wheat yields under no-till relative to conventional tillage, no-till farm profits improve by US$7 ha⁻¹ (US$3 ac⁻¹) on farms that produce only winter wheat and an average of US$2.50 ha⁻¹ (US$1 ac⁻¹) if averaged across all farms in the Fort Cobb Reservoir Watershed, including those that do not produce winter wheat. The study also finds that higher diesel prices, higher labor wages, lower herbicide costs, and smaller farm sizes are all relatively advantageous to no-till.

Refining crop and livestock management for dual-purpose spring canola (Brassica napus)

Dual-purpose canola (Brassica napus) describes the use of a canola crop for grazed winter forage before seed production, a practice that has only recently been developed in southern Australia. Long-season winter canola has been grazed without yield penalty in higher rainfall zones of Australia (>650 mm) and the USA, but the potential areas are small. The feasibility to graze spring canola varieties across wider areas of the medium-rainfall (450–650 mm), mixed-farming zone in Australia is therefore of interest. We conducted a series of six field experiments involving a range of canola cultivars and grazing management and agronomy systems from 2007 to 2009 at Young in southern New South Wales, Australia, to determine the feasibility of and refine the principles for grazing dual-purpose spring canola without significant yield penalty. Mid-season, Australian spring canola cultivars including conventional and hybrid varieties representing a range of herbicide tolerance (triazine-tolerant, Clearfield®, and Roundup Ready®) were sown from 16 April to 12 May and grazed with sheep at a range of growth stages from early vegetative (June) to mid-flowering (September). In general, early-sown crops (sown mid-April) provided significant grazing (~800 dry sheep equivalent grazing days/ha) in winter before bud elongation, and recovered with no impact on grain yield or oil content. As previously reported, yield was significantly reduced (by up to 1 t/ha) when grazing occurred after buds had elongated (late July), due to the delayed flowering associated with bud removal by sheep and insufficient time for biomass and yield recovery. However, yield was also reduced in crops grazed before bud elongation if insufficient residual biomass remained (<1.0 t/ha for late July lock-up) to facilitate crop recovery even when there was little delay in crop development. We suggest that refinements to the existing ‘phenology-based’ grazing recommendations would assist to avoid yield loss in grazed spring varieties, and propose three grazing stages (safe, sensitive, and unsafe) that integrate the impacts of time, crop growth stage, residual biomass, and seasonal conditions to avoid yield loss under different circumstances. Such refinements to reduce the likelihood of grazing-induced yield loss would provide more confidence for mixed farmers to maximise the benefits from dual-purpose canola in different environments. Based on the outcomes of these experiments, dual-purpose spring canola is likely to have significant potential for wider application in other mixed farming zones, with similar region-specific refinements based on the principles reported here.

Overexpression of AtLEAFY Accelerates Flowering in Brassica juncea

The floral meristem identity gene LEAFY (LFY) from Arabidopsis thaliana (L.) Heynh. can accelerate flowering in dicotyledonous plants. In this report, we raised transgenic plants of Brassica juncea (L.) Czern. cv. Varuna carrying the LEAFY gene (LFY) in sense and antisense orientation and studied the effect of modulation of LFY expression on flowering. The time required for the initiation of flowering was found to be reduced by 19% (∼1 wk earlier) in the transgenic plants overexpressing LFY as compared with the wild‐type untransformed control plants. Moreover, no significant yield penalty was observed in these transgenic plants. Altogether, these results open up the possibility of manipulating the flowering time in B. juncea without significant yield penalty or abnormalities.

Progress towards the understanding and control of sugar beet rhizomania disease.

Rhizomania is a soil-borne disease that occurs throughout the major sugar beet growing regions of the world, causing severe yield losses in the absence of effective control measures. It is caused by Beet necrotic yellow vein virus (BNYVV), which is transmitted by the obligate root-infecting parasite Polymyxa betae. BNYVV has a multipartite RNA genome with all natural isolates containing four RNA species, although some isolates have a fifth RNA. The larger RNA1 and RNA2 contain the housekeeping genes of the virus and are always required for infection, whereas the smaller RNAs are involved in pathogenicity and vector transmission. RNA5-containing isolates are restricted to Asia and some parts of Europe, and these isolates tend to be more aggressive. With no acceptable pesticides available to restrict the vector, the control of rhizomania is now achieved almost exclusively through the use of resistant cultivars. A single dominant resistance gene, Rz1, has been used to manage the disease worldwide in recent years, although this gene confers only partial resistance. More recently, new variants of BNYVV have evolved (both with and without RNA5) that are able to cause significant yield penalties on resistant cultivars. These isolates are not yet widespread, but their appearance has resulted in accelerated searches for new sources of resistance to both the virus and the vector. Combined virus and vector resistance, achieved either by conventional or transgenic breeding, offers the sugar beet industry a new approach in its continuing struggle against rhizomania.

Over-expression of a LEA gene in rice improves drought resistance under the field conditions

Late embryogenesis abundant (LEA) proteins have been implicated in many stress responses of plants. In this report, a LEA protein gene OsLEA3-1 was identified and over-expressed in rice to test the drought resistance of transgenic lines under the field conditions. OsLEA3-1 is induced by drought, salt and abscisic acid (ABA), but not by cold stress. The promoter of OsLEA3-1 isolated from the upland rice IRAT109 exhibits strong activity under drought- and salt-stress conditions. Three expression constructs consisting of the full-length cDNA driven by the drought-inducible promoter of OsLEA3-1 (OsLEA3-H), the CaMV 35S promoter (OsLEA3-S), and the rice Actin1 promoter (OsLEA3-A) were transformed into the drought-sensitive japonica rice Zhonghua 11. Drought resistance pre-screening of T(1) families at anthesis stage revealed that the over-expressing families with OsLEA3-S and OsLEA3-H constructs had significantly higher relative yield (yield under drought stress treatment/yield under normal growth conditions) than the wild type under drought stress conditions, although a yield penalty existed in T(1) families under normal growth conditions. Nine homozygous families, exhibiting over-expression of a single-copy of the transgene and relatively low yield penalty in the T(1) generation, were tested in the field for drought resistance in the T(2) and T(3) generations and in the PVC pipes for drought tolerance in the T(2) generation. Except for two families (transformed with OsLEA3-A), all the other families (transformed with OsLEA3-S and OsLEA3-H constructs) had higher grain yield than the wild type under drought stress in both the field and the PVC pipes conditions. No significant yield penalty was detected for these T(2 )and T(3) families. These results indicate that transgenic rice with significantly enhanced drought resistance and without yield penalty can be generated by over-expressing OsLEA3-1 gene with appropriate promoters and following a bipartite (stress and non-stress) in-field screening protocol.

Gains from improvement for mid-season drought tolerance in tropical maize ( Zea mays L.)

Drought and low soil fertility are major factors limiting maize production in the tropics. We examined the performance of hybrid progenies of drought-tolerant populations (DTP) in stressed (drought and low-N) and unstressed environments. A set of high-yielding normal single cross hybrids, developed using inbred lines improved with main emphasis on yield per se under optimal input conditions, was evaluated and compared with DTP c9 S 3 topcrosses across environments. Performance of normal hybrids was slightly better than DTP-topcrosses under unstressed conditions. However, under stress normal hybrids performed poorly with an average yield of 3.3–4.8% under drought and 34.8–36.2% under low-N stress. Hybrid progenies from DTP yielded up to 31.8–42.4% under drought and 48.9–63.6% under low-N as compared with their yields with out stress. Estimation of gains with selection for mid-season drought stress in DTPs over selection for improved yields under optimal input conditions showed that the gains were remarkable for drought (89.6%), and also for low-N stress (39.3%). The improved performance of DTP hybrids across environments was due to improvements in secondary traits such as reduced anthesis–silking interval, increased ears per plant, delayed senescence and relatively high leaf chlorophyll during late grain filling. Correlations between the performance of genotypes under drought and low-N stresses were positive and fairly high for DTP progenies, both white ( r 2=0.45 ∗,r=0.56 ∗ ) and yellow ( r 2=0.42 ∗,r=0.52 ∗ ), while it was not significant with normal hybrids. Selection for mid-season drought tolerance resulted in morpho-physiological changes that proved advantageous under both drought and low-N stress, without significant yield penalties under optimal input conditions.

Intercrops, Cicadulina spp., and maize streak virus disease

SUMMARYIntercrops of bean and finger millet were tested as a possible means of controlling maize streak virus disease (MSVD) in maize by disrupting the mating behaviour of the insect vectors of the maize streak virus, Cicadulina mbila and C. storeyi. A series of three trials were done. In the first, MSVD incidence 2 months after sowing was reduced to 14.9% and 17.4% in millet and bean intercrops compared to 29.5% in the pure maize stand. The number of male Cicadulina spp. caught on sticky pole traps was also significantly reduced relative to the control, but there was little effect on the catch of females. There was no significant yield penalty for the millet intercrop but maize yield was 49% lower in the bean intercrop treatment than in the pure stand. In the second trial, there were two millet and two bean intercrop treatments and a maize only control. Fewer male Cicadulina spp. were caught in the intercrop treatments relative to the control but MSVD incidence was reduced in one millet intercrop treatment only for which the associated maize yield penalty was 89%. In the final trial the bean intercrop was again tested but it had no effect on MSVD incidence. These experiments demonstrated that intercropping maize with bean or millet decreased vector activity and/or vector numbers. Vector catches were predominantly male, and catches of males but not females were reduced in the intercrop treatments compared with pure stands. However the lower vector catch was not consistently associated with a significant reduction in MSVD incidence, and when it was there was often an associated yield penalty in the maize due to the intercrop.