Histopathology comparison and phenylalanine ammonia lyase (PAL) gene expressions in Fusarium wilt infected watermelons

Fusarium wilt disease of watermelon (Citrullus lanatus (Thunb.) Matsum & Nakai), caused by Fusarium oxysporum f. sp. niveum (FON), is one of the limiting factors of worldwide watermelon production. In this study, a Fusarium wilt resistant watermelon JSB, which was derived from a spontaneous mutation of the susceptible Sugar Baby (SB), was used to investigate histopathology. The number and diameter of xylem vessels in the root (10 mm below the shoot base) of resistant JSB plants were significantly higher than those in susceptible SB plants. At 9 days post inoculation (dpi), using the plate assay on Nash-PCNB media, FON could be recovered from 86% of the roots in the symptomless plants of both watermelon lines, and from 55% and 64% of the stem segments (5 mm above the shoot base) in resistant and susceptible plants, respectively. In paraffin and free-hand tissue sections, at 8, 13, and 35 dpi, the xylem of roots and stems close to the soil surface in resistant watermelon JSB plants was also colonised by FON, but to a much lower percentage than the susceptible SB ones. No colonisation below the middle of stems was observed in the resistant JSB plants. The susceptible plants grown in infested soil were all dead by 35 dpi, while the resistant plants remained healthy. These observations suggest that reducing FON colonisation in the vascular systems of the host may contribute to the resistance in JSB. Furthermore, the higher expression of the phenylalanine ammonia lyase (PAL) gene in JSB induced by FON and the effects of PAL inhibitor on the resistance of JSB suggested that PAL is involved in resistance of watermelon to Fusarium wilt pathogen.

Development of SCAR markers linked to zt-2, one of the genes controlling absence of tannins in faba bean

Faba beans (Vicia faba L.) have a great potential as a protein-rich fodder crop, but anti-nutritional factors such as condensed tannins reduce the biological value of their protein. Tannins can be removed from seeds by any of the two complementary genes, zt-1 and zt-2, which also determine white-flowered plants. The less common gene, zt-2, is also associated with increased protein levels and energy values and reduced fibre content of the seeds. To identify a cost-effective marker linked to zt-2, we analysed a segregating F2 population derived from the cross between the coloured flower and high tannin content genotype Vf6 and a zt-2 line. By using Bulked Segregant Analysis (BSA), five RAPD markers linked in coupling and repulsion phase to zt-2 were identified and their conversion into Sequence Characterised Amplified Regions (SCARs) was attempted. Amplification of the SCARS was more consistent, although the initial polymorphism was lost. Restriction digestion of SCAR SCAD16589 with AluI (SCAD16-A), Bsp120I (SCAD16-B) and HinfI (SCAD16-H) revealed clear differences due to the amplification of different loci. The consensus sequence of these CAPs (Cleavage Amplification Polymorphisms) markers allowed discrimination of three bands from which two new forward SCAR primers were developed based on specific sequences from zero tannin and high tannin content genotypes. To improve the efficiency of the marker screening, a multiplex PCR was developed that allowed the simultaneous amplification of the SCAR with the same advantages as a codominant marker. Marker validation was carried out with a new F2 population segregating for flower colour and tannin content, underscoring the potential of these markers in breeding selection to introgress the zt-2 gene for the development of new tannin free faba bean cultivars.

Resistance to Phytophthora medicaginis Hansen and Maxwell in wild Cicer species and its use in breeding root rot resistant chickpea (Cicer arietinum L.)

Phytophthora root rot caused by Phytophthora medicaginis is a major disease of chickpea in Australia. Only partial resistance, derived from chickpea, is available in Australian cultivars. Five wild Cicer species were compared with chickpea cv. Jimbour (moderately resistant) in a field experiment. The proportions of accessions with significantly lower (P < 0.05) disease scores, where lower scores equate to higher resistance, were 9/9 for C. echinospermum, 9/21 for C. bijugum, 1/4 for C. judaicum, 1/29 for C. reticulatum, and 0/3 for C. pinnatifidum. The resistance of C. echinospermum (7/7 accessions) but not the other Cicer species was reproduced in a greenhouse test. Nine out of 30 chickpea × C. echinospermum-derived lines were as resistant as the C. echinospermum parents in a separate greenhouse experiment. C. echinospermum appears to be the best of the sources we examined for breeding chickpea cultivars resistant to P. medicaginis.

Comparing the phosphorus requirements of wheat, lupin, and canola

Spring wheat (Triticum aestivum L.), lupin (Lupinus angustifolius L.), and canola (Brassica napus L.) are the major crop species grown in rotation on the predominantly sandy soils of south-western Australia. Comparisons among the species for yield responses to applied phosphorus (P), effects of applied P on growth rates of shoots, P response efficiency for shoot and grain production, and the pattern for accumulation of P into shoots during growth and into grain at maturity are rare, or are not known, and were quantified in the glasshouse study reported here. Size and P content (P concentration multiplied by yield) of sown seed were in the order canola < wheat < lupin. Therefore, yield responses to applied P were first observed at ~10 days after sowing (DAS) for canola, ~17 DAS for wheat, and ~60 DAS for lupin. Lupin shoots showed no yield response to applied P at the first harvest at 51 DAS. Otherwise all species showed large yield, P concentration, and P content responses to applied P for all harvests at 51, 78, 87, 101, 121, and 172 DAS. To produce 90% of the maximum grain yield, the relevant data for cropping, lupin required ~67% less P than wheat, canola required ~40% less P than wheat, and canola required ~75% more P than lupin. Growth rates, and P response efficiency, were generally largest for canola, followed by wheat, then lupin. For shoots, P accumulation was in the order lupin > wheat > canola at 51 DAS, canola > wheat > lupin at 78 and 87 DAS, canola > wheat = lupin at 101 DAS, and all 3 species were about similar at 121 DAS. For accumulation of P into shoots plus grain at maturity (172 DAS) the order was canola > lupin > wheat, and for grain only was canola > wheat = lupin.

Male fertility restoration of wheat in Hordeum chilense cytoplasm is associated with 6HchS chromosome addition

We report a new cytoplasmic male sterility (CMS) source in bread wheat (Triticum aestivum L.) designated as msH1. CMS has been identified during the process of obtaining alloplasmic bread wheat in different Hordeum chilense Roem. Schultz. cytoplasms. It was observed that when using the H. chilense H1 accession, the corresponding alloplasmic line was male sterile. This alloplasmic wheat is stable under different environmental conditions and it does not exhibit developmental or floral abnormalities, showing only slightly reduced height and some delay in heading. On examining microsporogenesis in the alloplasmic line, it was found that different stages of meiosis were completed normally, but abnormal development occurred at the uninucleate-pollen stage at the first mitosis, resulting in failure of anther exertion and pollen abortion. Fertility restoration of the CMS phenotype caused by the H. chilense cytoplasm was associated with the addition of chromosome 6HchS from H. chilense accession H1. Thus, some fertility restoration genes appear to be located in this chromosome arm. Considering the features displayed by the msH1 system, we consider that it has a great potential for the development of viable technology for hybrid wheat production.

Adaptation of sulla cultivars to contrasting Mediterranean environments

Sulla coronaria (L.) Choi & Ohashi (syn. Hedysarum coronarium L.) may become a major forage species in various Mediterranean-climate areas. This study aimed to assess the extent of genotype × environment (GE) interaction in the western Mediterranean region and its implications for breeding programmes. The milestone Italian varieties Grimaldi and Sparacia, one recent Italian variety, and the Tunisian cv. D’Italie (evolved under moderately favourable conditions from Italian germplasm introduced about 40 years ago) were evaluated in three environments of Tunisia (of which two were irrigated), two of Algeria, and one of Sardinia (Italy). Water available over the crop cycle (rainfall + possible irrigation from October 2004 to June 2006), ranging from 881 to 1906 mm, accounted for 85% of the variation among environments and 72% of the GE interaction variation for dry matter yield. The latter was adequately described by one-covariate factorial regression, which was preferable to joint regression and additive main effects and multiplicative interaction modelling. D’Italie was specifically adapted to environments with available water exceeding 1200 mm, Grimaldi was top-ranking between 950 and 1200 mm, and Sparacia below 950 mm. The crossover GE interaction between top-yielding material (P < 0.05) has implications for adaptation targets, genetic resources, selection environments, and opportunities for international co-operation between breeding programmes. It suggests breeding either for rainfed cropping in semi-arid or near semi-arid environments, or for definitely subhumid or irrigated environments.

Developmental and physiological traits associated with high yield and stay-green phenotype in wheat

Water availability is a key limiting factor in wheat production in the northern grain belt of Australia. Varieties with improved adaptation to such conditions are actively sought. The CIMMYT wheat line SeriM82 has shown a significant yield advantage in multi-environment screening trials in this region. The objective of this study was to identify the physiological basis of the adaptive traits underpinning this advantage. Six detailed experiments were conducted to compare the growth, development, and yield of SeriM82 with that of the adapted cultivar, Hartog. The experiments were undertaken in field environments that represented the range of moisture availability conditions commonly encountered by winter crops grown on the deep Vertosol soils of this region. The yield of SeriM82 was 6–28% greater than that of Hartog, and SeriM82 exhibited a stay-green phenotype by maintaining green leaf area longer during the grain-filling period in all environments where yield was significantly greater than Hartog. However, where the availability of deep soil moisture was limited, SeriM82 failed to exhibit significantly greater yield or to express the stay-green phenotype. Thus, the stay-green phenotype was closely associated with the yield advantage of SeriM82. SeriM82 also exhibited higher mean grain mass than Hartog in all environments. It is suggested that small differences in water use before anthesis, or greater water extraction from depth after anthesis, could underlie the stay-green phenotype. The inability of SeriM82 to exhibit stay-green and higher yield where deep soil moisture was depleted indicates that extraction of deep soil moisture is important.

Effect of site, harvesting stage, and genotype on environmental staining in faba bean (Vicia faba L.)

Seed discoloration due to environmental staining in faba bean leads to poor quality and reduced market price. Environmental staining in faba bean is characterised by a dark brown, grey, or black discoloration of the seed coat at harvest. Its cause is unknown, but it does not appear to be caused by a pathogen. Environmental conditions during pod and seed formation and at maturity are thought to have a large effect on the degree of environmental staining. To test the hypothesis that seeds formed under stressful conditions will have a higher degree of staining, faba bean seeds were harvested at 2 different stages of maturity from trials located in a range of environmental conditions under a Mediterranean-type climate of south-western Australia over 2 seasons. Four faba bean varieties were studied (Fiord, Fiesta, Ascot, and Cairo). The majority of seeds had good colour but across the trials, 3–25% were stained up to an unacceptable level and this varied with location and variety. Seeds formed later in plant development (located on the upper nodes of the plant) had more staining than seeds formed earlier (located on the lower nodes). Seeds formed on small and weak plants had more staining than seeds formed on normal sized healthy plants. Fiord showed a greater amount of staining than Ascot, Fiesta, and Cairo when grown in the mild, southern environments. Early harvesting (at physiological maturity) did not reduce environmental seed staining compared with harvesting at full maturity. Chemical analysis of seed testa and cotyledons revealed that total phenolic contents of the testa and cotyledons increased with staining. An increase in Zn and Na and a decrease in K concentration in the testa were also associated with increased staining levels.

High crop productivity with high water use in winter and summer on the Liverpool Plains, eastern Australia

We report exceptional productivity and associated water-use efficiency across seasons for commercial crops of rainfed spring wheat and grain sorghum growing on stored soil water in Vertosols on the Liverpool Plains, central-eastern Australia. Agreement between the independently measured terms of evapotranspiration (ET) and the soil water balance (in-crop rainfall + δsoil water) was achieved within acceptable uncertainty across almost all measurement intervals, to provide a reliable dataset for the analysis of growth and water-use relationships without the confounding influence of water outflow either overland or within the soil. Post-anthesis intrinsic transpiration efficiency (kc ) values of 4.7 and 7.2 Pa for wheat and sorghum, respectively, and grain yields of 8 and 7 t/ha from ET of 450 and 442 mm (1.8 and 1.6 g/m2.mm), clearly demonstrate the levels of productivity and water-use efficiency possible for well-managed crops within an intensive and productive response cropping sequence. The Vertosols in which the crops were grown enabled rapid and apparently unconstrained delivery of significant quantities of subsoil water (34% and 51% of total available) after anthesis, which enabled a doubling of pre-anthesis standing biomass and harvest indices of almost 50%. Durum wheat planted into only 0.30 m of moist soil and enduring lower than average seasonal rainfall, yielded less biomass and grain (2.3 t/ha) with lower water-use efficiency (0.95 g/m2.mm) but larger transpiration efficiency, probably due to reduced stomatal conductance. We argue that crop planting in response to stored soil water and management for high water-use efficiency to achieve high levels of average productivity of crop sequences over time can have a significant effect on both increased productivity and enhanced hydrological stability across alluvial landscapes.

Relationships between carbon isotope discrimination and leaf morphophysiological traits in spring-planted spring wheat under drought and salinity stress in Northern China

The relationships between carbon isotope discrimination (Δ) and some morphophysiological traits such as specific leaf dry weight (SLDW), gas exchange parameters, and relative water content (RWC) were studied in a collection of 20 bread wheat cultivars (landraces, released cultivars and advanced lines) in three locations of the Ningxia region (North-East China), i.e. Yinchuan (limited irrigation conditions), Huinong (limited irrigation conditions + salinity) and Guyuan (rain-fed conditions). Relationships between Δ, grain yield (GY), and harvest index (HI) and above-ground biomass (AGB) were also analysed. Differences in the measured traits between different locations were highly related to the variation in water availability. Positive correlations were noted between Δ and HI and grain yield. Flag leaf Δ was positively correlated with RWC at anthesis, and negatively associated with SLDW at grain filling. Significant and negative correlations between Δ and dry matter weight per plant at anthesis and biomass at maturity were noted. Leaf temperature (LT) was found to be negatively correlated with Δ and gs. The findings suggest that Δ may be a useful indicator reflecting wheat yield, harvest index, and water status under irrigation and rain-fed conditions in the Ningxia region.