Brassica Genotypes Research Articles

Pathogenicity of morphologically different isolates of Sclerotinia sclerotiorum with Brassica napus and B. juncea genotypes

Sclerotinia stem rot caused by Sclerotinia sclerotiorum is a serious threat to oilseed production in Australia. Eight isolates of S. sclerotiorum were collected from Mount Barker and Walkway regions of Western Australia in 2004. Comparisons of colony characteristics on potato dextrose agar (PDA) as well as pathogenicity studies of these isolates were conducted on selected genotypes of Brassica napus and B. juncea. Three darkly-pigmented isolates (WW-1, WW-2 and WW-4) were identified and this is the first report of the occurrence of such isolates in Australia. There was, however, no correlation between pigmentation or colony diameter on PDA with the pathogenicity of different isolates of this pathogen as measured by diameter of cotyledon lesion on the host genotypes. Significant differences were observed between different isolates (P ≤ 0.001) in two separate experiments in relation to pathogenicity. Differences were also observed between the different Brassica genotypes (P ≤ 0.001) in their responses to different isolates of S. sclerotiorum and there was also a significant host × pathogen interaction (P ≤ 0.001) in both experiments. Responses between the two experiments were significantly correlated in relation to diameter of cotyledon lesions caused by selected isolates (r = 0.79; P < 0.001, n = 48). Responses of some genotypes (e.g., cv. Charlton) were relatively consistent irrespective of the isolates of the pathogen tested, whereas highly variable responses were observed in some other genotypes (e.g., Zhongyou-ang No. 4, Purler) against the same isolates. Results indicate that, ideally, more than one S. sclerotiorum isolate should be included in any screening programme to identify host resistance. Unique genotypes which show relatively consistent resistant reactions (e.g., cv. Charlton) across different isolates are the best for commercial exploitation of this resistance in oilseed Brassica breeding programmes.

Maintenance of stress related transcripts in tolerant cultivar at a level higher than sensitive one appears to be a conserved salinity response among plants

Response of plants towards salinity is multigenic in nature with its various components playing diverse roles in stress perception, relay or response. For the purpose of dissecting the genetic determinants of salinity response in crops, the family Brassicaceae presents an excellent model since significant inter- and intra-specific variations have been reported for salinity tolerance. Using these intraspecific variations of Brassica, we show that one of the possible mechanism by which a genotype is able to exhibit tolerance better than another is by keeping the basal levels of stress responsive transcripts higher than the sensitive genotype. This is quite reflected when we analyze members of a specific pathway such as SOS pathway or even when we extend the analysis to a range of molecules including those playing important role in stress perception, signal transduction or stress response. However, these investigations need to be extended to genome level transcript analysis to further validate the hypothesis of “well preparedness” in tolerant genotypes and we propose the suitability of Brassica genotypes for this endevors.

Induction of thermotolerance through heat acclimation and salicylic acid in Brassica species

High temperature stress is the second most important stress, which can strike crop plants at any time and impose severe limitations on crop growth and development. Developing crop plants with improved thermotolerance can mitigate the adverse effects of heat stress. However, a thorough understanding of physiological responses of plants to high temperature and mechanisms involved for thermotolerance is imperative. Brassica is an important oilseed crop and its early sowing implies many important advantages. However, the crop sown early encounters high temperature stress, which causes a great yield lost. Many putative signaling molecules like SA, ABA, H2O2 and CaCl2 and heat acclimation have been found to be involved in inducing thermotolerance as well as in initiating the underlying signal transduction pathway for upregulating various genes involved in thermotolerace. In the present investigation, we observed the effects of heat shock, heat acclimation and SA in four genotypes of Brassica; TL15, PBT37, RL1359 and PBR210. Heat acclimation for 3 h at sublethal temperature and SA pretreatments at 10 and 20 iM for 2 h prior to heat shock were found to be effective in imparting thermoprotection at seedling stage, which is the crucial stage of plant establishment. These pretreatments helped seedlings to recover from heat stress by increasing seedling length, reduced electrolyte leakage and conferring membrane protection. Increased level of total soluble sugars, fresh/dry weight, and also increase in enzymatic activities of invertase, CAT, POX conferred thermotolerance. Further, enhanced expression of some new proteins including heat shock proteins (HSPs) was observed by both of the pretreatments through SDS-PAGE. We assume that heat acclimation and SA pretreatments induced thermotolerance and definitely play a role in initiating various mechanisms involved in overcoming high temperature limitations.

Towards salinity tolerance in Brassica: an overview

Among the various abiotic stresses limiting the crop productivity, salinity stress is a major problem, which needs to be addressed and answered urgently. Since members of Brassicaceae are important contributor to total oilseed production, there is an immediate need being felt to raise Brassica plants which would be more suitable for saline and dry lands in years to come. One of the suggested way to develop salinity tolerant Brassica plants is to make use of the broad gene pool available within the family. Efforts of breeders have been successful in such endeavors to a large extent and several salinity tolerant Brassica genotypes have been developed within India and elsewhere. On the other hand, transgenic technology will undoubtedly continue to aid the search for the cellular mechanisms that confer tolerance, but the complexity of the trait is likely to mean that the road to engineer such tolerance into sensitive species will not be easy. However, with increasing number of reports available for suitable genetic transformation for various Brassica genotypes, there is a hope that salinity tolerance can be improved in this important crop plant. In this direction, the complete genome sequence of related wild plants such as Arabidopsis or crop plants such as rice can also serve as a platform for identification of "candidate genes". Recently, complete genome sequencing of the Brassica genomes has also been initiated with the view that availability of such useful information can pave way towards raising Brassica with improved tolerance towards these stresses. In the present paper, we discuss the success obtained so far; in raising brassica genotypes with improved salinity tolerance employing both plant breeding and/or genetic engineering tools.

Cotyledon assay as a rapid and reliable method of screening for resistance againstSclerotinia sclerotioruminBrassica napusgenotypes

Sclerotinia sclerotiorum is a major pathogen of many crops, including oilseed rape (Brassica napus), and there is keen interest worldwide to identify Brassica genotypes with resistance to this pathogen. However, field testing to identify resistance in B. napus germplasm is expensive, time-consuming and at times unreliable due to variability in field environmental conditions and plant architecture. To address this, we aimed to examine the feasibility of utilising for B. napus a cotyledon test already developed for Sclerotinia disease on legumes. Initially, cotyledons of 32 B. napus genotypes were drop-inoculated using macerated mycelium (104 mycelial fragments/mL) under controlled environmental conditions. Significant differences were recorded between B. napus genotypes, and the experiment was repeated twice using genotypes selected from the first experiment. Certain genotypes responded with a distinct hypersensitive reaction (lesions <1 mm diameter), either always (cv. Mystic) or frequently (cv. Charlton), which is the first report of this phenomenon in the B. napus-S. sclerotiorum pathosystem. Responses of genotypes between the three screening experiments were significantly and positively correlated. Results obtained in the first experiment were compared with those from our earlier field screening for stem rot that utilised the same strain of S. sclerotiorum and the same B. napus genotypes. In particular, there was a significant positive correlation (r=0.62, P < 0.01) between published field data for stem rot and our cotyledon test results across genotypes in common. This indicates the usefulness of this cotyledon assay to provide a relatively reliable indication of field performance of genotypes. We believe that this is the first report demonstrating that a cotyledon assay can be successfully applied to rapidly differentiate the reactions of B. napus genotypes against S. sclerotiorum.

Short communication. Harvest stage effects on forage yield and quality for rape and turnip genotypes

The effects of two different harvest stages (full flowering and full podding) on forage yield and quality of ten forage rape (Brassica napus L. var. oleifera) and three turnip (Brassica rapa L. var. rapa) cultivars were evaluated under rainfed conditions in a Mediterranean type climate at Bursa, Turkey, during the 2002/2003 and 2003/2004 growing seasons. Plant height, branches per plant, leaf length and width, plant part components, and dry matter (DM) and crude protein (CP) yield were measured. Significant differences were observed for the main effects cultivar and harvest stage on DM and protein yields. The CP content of the whole plant and vegetative parts of the Brassica genotypes decreased as plant maturity progressed. In general, turnip cultivars showed better performance in DM yield. Fall sown turnip produced 9.10 and 12.1 Mg/ha DM yield, with 15.1 and 9.10% CP concentrations, at full flowering and at podding stage, respectively. Significant differences were noted among cultivars for these two parameters. Protein content decreased dramatically in stem parts when maturity advanced from full flower to full pod stages. High leaf percentage and high protein content at full flowering suggest that this should be the preferred forage harvest stage for rape and turnip cultivars.

Resistance to cabbage seedpod weevil among selected Brassicaceae germplasm

AbstractBrassicaceae germplasm (Brassica napus L., Brassica rapa L., Brassica juncea (L.) Czern., Brassica carinata A. Braun, Sinapis alba L., Camelina sativa (L.) Crantz, Crambe species) with cultivar development potential for the prairies was evaluated for resistance to cabbage seedpod weevil (Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae)) infestation under field conditions in southern Alberta from 2001 to 2005. Relative susceptibilities were as follows: B. rapa and B. napus &gt; B. juncea = B. carinata &gt; S. alba. Although some of the germplasm evaluated varied within species in terms of glucosinolate profile, erucic acid level, oil content, and plant height, none of these factors appeared to influence the degree of C. obstrictus damage. A subset of this germplasm was also evaluated in the greenhouse. Although the canola species B. rapa sustained the highest level of damage in the field tests, it was similar to other Brassica genotypes in the greenhouse. All lines of S. alba were virtually immune to weevil attack in both field and greenhouse tests, regardless of glucosinolate profile, suggesting that other factors confer resistance in this species. Synchrony of crop development with weevil activity in the field explains some of the variability in damage observed among genotypes and illustrates the importance of combining field and greenhouse studies when assessing resistance.

Characterization of Cysteine‐Degrading and H2S‐Releasing Enzymes of Higher Plants ‐ From the Field to the Test Tube and Back

Due to the clean air acts and subsequent reduction of emission of gaseous sulfur compounds sulfur deficiency became one of the major nutrient disorders in Northern Europe. Typical sulfur deficiency symptoms can be diagnosed. Especially plants of the Cruciferae family are more susceptible against pathogen attack. Sulfur fertilization can in part recover or even increase resistance against pathogens in comparison to sulfur-deficient plants. The term sulfur-induced resistance (SIR) was introduced, however, the molecular basis for SIR is largely unknown. There are several sulfur-containing compounds in plants which might be involved in SIR, such as high levels of thiols, glucosinolates, cysteine-rich proteins, phytoalexins, elemental sulfur, or H2S. Probably more than one strategy is used by plants. Species- or even variety-dependent differences in the development of SIR are probably used. Our research focussed mainly on the release of H2S as defence strategy. In field experiments using different BRASSICA NAPUS genotypes it was shown that the genetic differences among BRASSICA genotypes lead to differences in sulfur content and L-cysteine desulfhydrase activity. Another field experiment demonstrated that sulfur supply and infection with PYRENOPEZIZA BRASSICA influenced L-cysteine desulfhydrase activity in BRASSICA NAPUS. Cysteine-degrading enzymes such as cysteine desulfhydrases are hypothesized to be involved in H2S release. Several L- and D-cysteine-specific desulfhydrase candidates have been isolated and partially analyzed from the model plant ARABIDOPSIS THALIANA. However, it cannot be excluded that H2S is also released in a partial back reaction of O-acetyl-L-serine(thiol)lyase or enzymes not yet characterized. For the exact determination of the H2S concentration in the cell a H2S-specific microsensor was used the first time for plant cells. The transfer of the results obtained for application back on BRASSICA was initiated.

Comparative Evaluation of RAPD, ISSR and Anchored-SSR Markers in the Assessment of Genetic Diversity and Fingerprinting of Oilseed Brassica Genotypes

Forty-two genotypes representing oilseed Brassica species were analyzed for the level of genetic diversity and molecular identity using Random Amplified Polymorphic DNA (RAPD), Inter-Simple Sequence Repeat (ISSR) and 5'-Anchored Simple Sequence Repeat (ASSR) markers. DNA profiles revealed high degree of interspecific polymorphism, while the level was considerably low within a species, particularly in B. juncea. The UPGMA clusters clearly delineated genotypes of the respective Brassica species. Comparison of cophenetic matrices indicated a high degree of correspondence between dendrograms generated by different marker systems. A minimum of 10 random primers (approximately 105 bands) were required for the RAPD profiles to generate the expected cluster. Comparatively less number of primers was required to do the same in case of ISSR (4 primers) and ASSR (3 primers). The principal component analysis revealed similar genetic relationship among the genotypes as in cluster analysis. Although none of the DNA profiles could individually identify all the B. juncea genotypes, a combined DNA profile consisting 125 markers from the informative primers of all the three DNA marker systems could do the same. A positive correlation was found among the marker utility parameters (calculated for individual primers of different marker systems) such as marker index (MI), resolving power (Rp) and discrimination coefficient (D) with the number of genotypes identified by each primer with a few exceptions. Single plant analysis for a set of five B. juncea varieties revealed absence of intra-varietal heterogeneity in case of ASSR profiles, thereby suggesting its utility in varietal identification and differentiation.

Belowground interactions between intercropped wheat and Brassicas in acidic and alkaline soils

Our previous studies showed that, under P-limiting conditions, growth and P uptake were lower in the wheat genotype Janz than in three Brassica genotypes when grown in monoculture. The present study was conducted to answer the question if P mobilised by the Brassicas is available to wheat; leading to improved growth of wheat when intercropped with Brassicas compared to monocropped wheat. To assess if the interactions between the crops depend on soil type, the wheat genotype Janz and three Brassica genotypes (two canolas and one mustard) were grown for 6 weeks in monoculture or wheat intercropped with each Brassica genotype in an acidic and an alkaline soil with low P availability (with two plants per pot). Wheat grew equally well in the two soils, but the Brassicas grew better in the acidic than in the alkaline soil. In the acidic soil, monocropped Brassicas had a 3 to 4 fold greater plant dry weight (dw) and P uptake than wheat; plant dw and P uptake in wheat were decreased or not affected by intercropping and increased in the Brassicas. In the alkaline soil, dw and P uptake of the Brassicas was twice as high as in wheat, with intercropping having no effect on these parameters. The contribution of wheat to the total shoot dw and P uptake per pot was 4–21% and 32–40% in acidic and alkaline soil, respectively. Mycorrhizal colonisation was low in all genotypes in the acidic soil (1–6%). In the alkaline soil, mycorrhizal colonisation of monocropped wheat was 62%, but only 43–47% in intercropped wheat. Intercropping decreased P availability in the rhizosphere of wheat in the acidic soil but had no effect on rhizosphere P availability in the alkaline soil. Intercropping had a variable effect on rhizosphere microbial community composition (assessed by fatty acid methylester analysis (FAME) and ribosomal intergenic spacer amplification (RISA)), ranging from intercropping having no effect on the rhizosphere communities to intercropping resulting in a new and similar rhizosphere community composition in both genotypes. The results of this study show that intercropping with Brassicas does not improve growth and P uptake of wheat; thus there is no indication that P mobilised by the Brassicas is available to wheat.

Brassica genotypes differ in growth, phosphorus uptake and rhizosphere properties under P-limiting conditions

Compared to other crops, Brassicas are generally considered to grow well in soils with low P availability, however, little is known about genotypic differences within Brassicas in this respect. To assess the role of rhizosphere properties in growth and P uptake by Brassicas, three Brassica genotypes (mustard, Brassica juncea cv Chinese greens and canola, Brassica napus cvs Drum and Outback) were grown in an acidic soil with low P availability at two treatments of added P: 25 and 100 mg P kg −1 as FePO 4 (P25 and P100). The plants were harvested at the 6-leaf stage, at flowering and at maturity. Shoot and root dry weight (dry weight) and root length increased with time and were lower in P25 than in P100. In P25, shoot dry weight was lowest in Outback and highest in Chinese greens. In the P100 treatment, Chinese greens had a higher shoot dry weight than the two canola cultivars. Chinese greens had a lower root dry weight and root length at flowering and maturity than the canola genotypes in both P treatments. Irrespective of P treatment, shoot P concentration was lower in Chinese greens than in the two canola genotypes. Specific P uptake (μg P m −1 root length) decreased with time. In P25, Chinese greens had the lowest specific P uptake at the 6-leaf stage but it was higher than in the two canola genotypes at flowering and maturity. In P100, Outback had the lowest specific P uptake. Available P in the rhizosphere (resin P) decreased over time with the greatest decrease from the 6-leaf stage to flowering. In P25, resin P in the rhizosphere was greatest in Chinese greens at the 6-leaf stage and flowering and smallest in Outback at flowering. Microbial P and acid phosphatase activity changed little over time, were not affected by P treatment and there were only small differences between the genotypes. The rhizosphere microbial community composition [assessed by fatty acid methyl ester (FAME) analysis] of Outback and Chinese greens differed from that of the other two genotypes at the 6-leaf stage and flowering, respectively. At maturity, all three genotypes had distinct microbial communities. Plant traits such as production of high biomass at low shoot P concentrations as well as the capacity to maintain high P availability in the rhizosphere by P mobilisation can explain the observed differences in plant growth and P uptake among the Brassica genotypes.

Strains of Leptosphaeria maculans with the Capacity to Cause Crown Canker on Brassica carinata are Present in Western Australia.

Blackleg, caused by Leptosphaeria maculans (Desm.) Ces. et de Not., is the most important disease of canola (Brassica napus L.) in Australia, Europe, Canada, and North America (2). During the early 1990s, new cultivars of canola with resistance to blackleg were released in Australia. Despite good adult-plant resistance, these cultivars still suffered significant yield losses from blackleg under high disease pressure. Potential new sources of blackleg resistance such as B. nigra L., B. carinata L., and Sinapis alba L. are being evaluated. B. carinata is believed to be highly resistant to blackleg by virtue of its B-genome. However, some L. maculans isolates that can attack B. carinata have been reported from Germany (1). During the 2003 growing season, 22 isolates of L. maculans were collected from different canola-growing areas of Western Australia and tested for their reaction on 24 seedlings of each of various Brassica genotypes, including B. carinata, in a controlled environment chamber. Twenty-four seeds per genotype were sown in 100-ml plastic pots (12 seeds per pot) and both cotyledons of 10-day-old seedlings were wound inoculated with a conidial suspension (1 × 107 conidia/ml) of each isolate of L. maculans. Disease assessments were made 2 weeks after inoculation. The majority of isolates induced a noninvasive hypersensitive reaction on B. carinata without pycnidial development. However, four of the isolates caused lesions with abundant pycnidia on B. carinata cotyledons. The lesion size ranged between 3 and 7 mm and appeared similar to that on susceptible B. napus cultivars. B. carinata seedlings were grown for another 8 weeks in a glasshouse, and crown cankers were observed from plants inoculated with three of the four seedling virulent isolates. The severity of crown cankers as percent of stem circumference (percent disease index) ranged between 20 and 54%. Twenty-five stem pieces from mature B. carinata plants infected with one of the three isolates were plated on V8 juice agar and L. maculans was recovered from 70% of pieces. Abundant pycnidia were also observed on these stem pieces. These results have important implications for using B. carinata as a source of blackleg resistance in canola breeding. To our knowledge, this is the first report of L. maculans isolates with the capacity to induce crown cankers on B. carinata in Australia.

Phytotoxicity of cadmium and its effect on two genotypes of Brassica juncea L.

By using two Brassica juncea, L. (Indian mustard) genotypes (Varuna and DHR-9504) agreenhouse experiment was carried out to study the effect of cadmium (Cd) on growth, yield and concentration of cadmium (Cd) in different plant parts at the Agricultural Research Station, Bilaspur Chhattisgarh, India during 2002-2003. Plants were grown under controlled climatic conditions and subjected to increasing Cd supply in the form of CdCl2 @ 0, 20, 40, 60, 80 and 100 mg Cd kg-1 soil. Cdphytotoxicity was shown by growth retardation of Varuna and DHR-9504. Varuna showed greater sensitivity to Cd toxicity than DHR-9504. Increasing Cd supply markedly reduced the seed, stem and root dry weight of both genotypes (Varuna and DHR-9504), and these decreases were more marked in Varuna.Due to increased level of Cd application, the Cd concentration increased significantly in various plant parts in both the Brassica genotypes tested. Increase in Cd concentration of about 5 times in seeds, 7 times in stems and 9 times in roots was noted with an application of 20 mg Cd kg-1 soil more than the control. Cd was accumulated in the roots in much higher amounts than in the stem and seeds, especially in the case of DHR-9504, indicating that there is limited transport of Cd from the root system to the above ground plant parts in DHR-9504 genotype due to the presence of strong Cd-binding proteins in the roots. GenotypeDHR-9504 had significantly less uptake of Cd than genotype Varuna. More data are needed to ascertain the findings of this study.

Differential tolerance of high manganese among rapeseed genotypes

Cultivation of crop cultivars resistant to high soil manganese (Mn) may reduce the negative effects of Mn toxicity on crop yield. Three studies were carried out to select Brassica genotypes (B. napus and B. rapa) resistant to high Mn concentration and to characterise the nature of any Mn resistance found. In Experiment 1, 33 B. napus and nine B. rapa genotypes were screened in a sub-irrigated nutrient solution system. Based on visual symptoms and plant size, single plants were identified with resistance to high Mn from within cultivars of four B. napus and one B. rapa. Resistance was also identified in one B. napus doubled haploid genotype. In Experiment 2, a genotype resistant to high Mn and two genotypes (progenies from Experiment 1) sensitive to high Mn were exposed to eight Mn concentrations (9–500 μM) for 2 weeks in nutrient solution. The relative shoot weight (RSW) and the relative root weight (RRW) of the genotype resistant to Mn were significantly greater at ≥100 μM Mn than both genotypes sensitive to high Mn; the sensitive genotypes reacted similarly. The three genotypes had similar tissue Mn contents and the elevated Mn tissue contents did not induce deficiencies of Mg or Fe. In Experiment 3, 12 genotypes (progenies from Experiment 1) were screened in nutrient solution at 9 μM Mn and with an additional 125 μM Mn. The RRW and RSW of the genotypes ranged from 35 to 114 and 39 to 94%, respectively. All the selections sensitive to high Mn had a RSW 70% and thus were confirmed as Mn resistant. This evidence confirmed the availability of rapeseed germplasm resistant to Mn toxicity with an ability to withstand high content of Mn through internal tissue tolerance. Also, the observed Mn tolerance in this material is genetically controlled and not an artifact of our screening assays.

Cytoplasmic effects on photosynthesis and ribulose-1,5-bisphosphate carboxylase activity in Brassica species

Brassica genotypes representing four different species viz. B. nigra and B. campestris (both primary diploids), B. juncea and B. carinata (both allotetraploids) were examined for photosynthesis rate (Pn), ribulose-1,5-bisphosphate carboxylase (RuBPC) activity, leaf soluble protein and chlorophyll content. B. nigra is the male and female parent of B. juncea and B. carinata, respectively. B. campestris is the maternal parent of B. juncea. Pn was significantly higher in B. nigra and B. carinata compared to the other two species. These two species also sustained Pn of the leaves for a longer period during ontogeny. When B. nigra was the male parent, the higher Pn of B. nigra was not inherited in B. juncea. On the other hand, the Pn and pattern of ontogenetic changes in B. campestris and B. juncea were more or less similar. In specific RuBPC activity on soluble protein basis, chlorophyll and soluble protein content B. carinata also followed B. nigra whereas, B. juncea followed B. campestris. These results indicated the possible maternal(cytoplasmic) influence on the inheritance of these traits.

RESISTANCE TO XANTHOMONAS CAMPESTRIS PV. CAMPESTRIS IN BRASSICA SPP.

Six races of Xanthomonas campestris pv. campestris have been identified on the basis of their reactions on a series of differential Brassica genotypes. Races 1 and 4 are the most important races worldwide. Searches for resistance in a collection of Brassica oleracea (C genome) were mainly unsuccessful, but partial or total resistance to races 2, 3, 5 and 6, which are rare races, was present in a number of accessions. Strong resistance to race 4 was widespread in B. rapa (A genome) and B. napus (AC genome) indicating an A genome origin. Resistance to races 1, 3 and 4 was found in B. nigra (B genome), B. carinata (BC genome) and B. juncea (AB genome) suggesting a B genome origin. Potential race non-specific resistance was also found in these three species and in B. rapa. Resistance to races 1 and 3 is quantitative and recessive in the cabbage line Badger Inbred-16, while resistance to race 3 is controlled by a single dominant locus in several B. oleracea lines. Resistance to race 4 is controlled by a single dominant locus in B. napus and probably in B. rapa. Resistance to races 1, 3 and 4 appears to be dominant in B. nigra and B. carinata.

Photosynthesis and its related physiological variables in the leaves of Brassica genotypes as influenced by sulphur fertilization

In the present investigation, we examined the effect of sulphur fertilization on photosynthesis (Pn) and its related physiological variables in the leaves of field grown Brassica genotypes (Brassica juncea [L.] Czern. and Coss. cv. Pusa Jai Kisan and Brassica campestris L. cv. Pusa Gold) over a whole growing season. Sulphur fertilization significantly (P&lt;0.05) increased the Pn rate on leaf area basis at all the growth stages over −S treatment. The photosynthesis related variables such as soluble protein and Rubisco (ribulose‐1,5‐bisphosphate carboxylase/oxygenase) protein were significantly higher in the leaves of plants grown with +S treatment, when compared to −S treatment. Sulphur fertilization also improved the chlorophyll, N and S content in the leaves of +S treated plants over −S treatment. Leaf‐S content was linearly correlated with Pn rate, N‐content and Rubisco protein in the leaves of both genotypes. An interesting relationship between N‐content and Pn rate in the leaves of −S and +S treated plants was observed. In −S plants, the relationship between Pn rate and N‐content per unit area of fully matured leaves became non‐linear when leaf‐N exceeded 1.5 g m−2, while in +S plants the same remained linear. Rubisco protein was linearly related to Pn rate and leaf‐N content. The ratio of Rubisco/soluble protein was lesser in the leaves of −S treated plants than +S treated plants. The effect of sulphur fertilization on Pn is discussed in relation to improved nitrogen utilization efficiency of the plants that leads to incorporation of reduced‐N into the protein, especially in Rubisco protein rather than the non‐protein compounds.

Effect of split application of sulphur and nitrogen on growth and yield attributes of Brassica genotypes differing in time of flowering

According to prevalent agronomic practices for cultivation of Brassica genotypes, N is applied in split doses, while S is applied as a basal dose. This may create imbalance in the supply of these nutrients during the growth and development of the crop because metabolism of N and that of S are closely linked and play a central role in protein synthesis. The requirement of one depends on the supply of the other, and the imbalance in their supply causes a reduction in the yield because of reduced uptake and assimilation of the two nutrients. In the present investigation, therefore, S was applied in split doses, along with N, to study its effect on growth and yield attributes of Brassica juncea (L.) Czern. and Coss. (V1) and Brassica campestris L. (V2). In the experiment, conducted in the field, 40 kg S ha−1 as CaSO4 (gypsum) was applied either in a single basal application (S1) or in two (S2) or three (S3) split applications; and 100 kg N ha−1 as urea was applied either in two (N2) or three (N3) splits. Biomass accumulation, leaf-area index (LAI), leaf-area duration (LAD), crop growth rate (CGR) and photosynthesis in the leaves were determined at various phenological stages. Split application of S and N (S2N2 or S3N3) resulted in significant improvement in growth and yield of both the genotypes compared with the application of S in a single basal application and N in two splits (S1N2). Genetic variability was observed between the two genotypes in response to split application of S and N. V1 responded better when S and N was applied in two split doses (S2N2) than when it was applied as S1N2 or S3N3 This S2N2 treatment resulted in 40.0, 39.7, 35.5, 48.2 and 18.1% enhancement in biomass accumulation, LAI, LAD, CGR and photosynthetic rate, respectively in comparison with S1N2. Seed yield, biological yield and harvest index were improved by 38.3, 26.3 and 9.5%, respectively, by S2N2 over the results obtained with S1N2. In the case of V2, three split applications of S and N (S3N3) resulted in maximum growth and yield. Increases in biomass accumulation, LAI, LAD, CGR and photosynthetic rate due to application of S3N3 were 48.4, 81.3, 77.9, 101.1 and 28.6% respectively, over the results of S1N2. Seed yield, biological yield and harvest index improved by 41.3, 26.9 and 11.6% respectively, with this treatment.On the basis of results obtained in this study, it can be concluded that S must be applied in split doses for optimum growth and yield of Brassica genotypes. The variability in response of these genotypes to split application of S and N was due to differences in flowering time, as V1 flowered earlier (just after the application of the second dose of S and N) than V1 (just after the application of the third dose of S and N). Key words: Brassica genotypes, nitrogen, sulphur, split application, growth, yield

Resistance of Brassica, especially B. juncea (L.) Czern, genotypes to the diamondback moth, Plutella xylostella (L.)

Resistance of Brassica, especially B. juncea (L.) Czern, genotypes to the diamondback moth (DBM), Plutella xylostella (L.), was evaluated in growth room studies in Saskatoon, Canada, and in field studies at Angunakolapelessa, Sri Lanka. Growth room studies of DBM oviposition preference on 33 genotypes of Brassica showed that Cutlass, Rahangala Sp-2, MI Sp-3 and Kudaoya Sp-11 ( B. juncea), Echo [ B. rapa (L.)], S-67 [ B. carinata (Braun)], Vates [ B. oleracea (L.)] and Nilla [ B. napus (L.)] were the least preferred hosts. These genotypes were field-tested in two cropping seasons under insecticide-treated and untreated conditions. Counts of DBM eggs and larvae showed that Rahangala Sp-2 and Vates were most resistant to DBM, whereas Cutlass was moderately resistant. Further, these three genotypes were the least damaged by DBM larvae. Rahangala Sp-2 and Cutlass represent the first sources of resistance to DBM identified in B. juncea. It is suggested that Rahangala Sp-2, Vates and Cutlass may serve as sources of resistance to DBM and prove useful in genetic improvement programs for resistance to this major pest of brassicaceous crops.

Involvement of SLR1 genes in pollen adhesion to the stigmatic surface in Brassicaceae

The S-locus-related gene SLR1 is highly conserved and highly expressed in several species of the Brassicaceae family. Its function has not been determined, although several features would suggest a fundamental role in pollination. A second related gene (SLR2) is conserved and expressed in a subset of Brassica genotypes. We analysed the stigmatic expression of SLR1 and SLR2 genes among 11 different plants from various species or genera of the Brassicaceae and examined the extent of the pollen-stigma interaction during intraspecific, interspecific and intergeneric pollinations between them. Appropriate statistical tests on these variables (pollen adhesion, germination, penetration into the stigma, style and ovary, and SLR gene expression) showed that expression of SLR1 (but not SLR2) may be a factor in pollen-stigma adhesion. This hypothesis was supported by the observation of reduced pollen-stigma adhesion in transgenic B. napus plants modified for SLR1 expression.