Genetic combining ability of glucoraphanin level and other horticultural traits of broccoli

Broccoli (Brassica oleracea L., Italica Group) is a source of glucosinolates and their respective isothiocyanate metabolites that are believed to have chemoprotective properties in humans. Glucoraphanin (4-methylsulfinyl-butyl glucosinolate) is a predominant glucosinolate of broccoli. Its cognate isothiocyanate, sulforaphane, has proven a potent inducer of phase II detoxification enzymes that protect cells against carcinogens and toxic electrophiles. Little is known about the genetic combining ability for glucosinolate levels or the types of genetic variation (i.e., additive vs. dominance) that influence those levels in broccoli. In this study, a diallel mating design was employed in two field experiments to estimate combining abilities for glucoraphanin content. The diallel population was developed by crossing nine doubled-haploid (inbred) parents in all possible combinations (36), excluding the reciprocals. Horticultural traits of all entries were assessed on a plot basis. In fall 2001, glucoraphanin concentration of broccoli heads ranged from 0.83 to 6.00 μmol/gdw, and in spring 2002, ranged from 0.26 to 7.82 μmol/gdw. In both years, significant general combining ability was observed for glucoraphanin concentration and total head content, days from transplant to harvest, head weight, and stem diameter. Conversely, no significant specific combining ability was observed for any trait in either year. Results indicate that a given inbred will combine with others to make hybrids with relatively predictable levels of head glucoraphanin as well as, other important horticultural traits. This should allow identification of inbreds that typically contribute high glucoraphanin levels when hybridized with others.Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.     

Combined effects of soil silicon and drought stress on host plant chemical and ultrastructural quality for leaf-chewing and sap-sucking insects

It was postulated that Si-mediated plant resistance to herbivory changes with soil water status, increasing when plants are under drought stress. We subjected collard (Brassica oleracea) to such soil variables and assessed plant responses and effects on the leaf-chewing larvae of Plutella xylostella and the sap-sucking aphid Brevicoryne brassicae. Silicon accumulated in collard leaves independently of soil water conditions, but it influenced mainly drought-stressed plants. Silicon suppressed harmful effects of drought on leaf and root length and raised leaf water content and stomatal size to the same conditions of well-watered plants. Drought stress reduced hemicellulose and cellulose, but Si did not influence them or lignin. Combination of drought and Si increased total and soluble leaf nitrogen. Drought decreased total glucosinolates, but Si increased such defence metabolites to similar concentrations that were found in well-watered plants. Nutritional changes mediated by drought and Si in fibre, leaf water content, soluble nitrogen and glucosinolates did not increase insect performance in any feeding guild. Instead, caterpillars performed worse in drought-stressed or Si-treated collards, mainly in plants under combined conditions. Silicon improved plant resistance to drought and herbivore stresses.     

Suitability of A European Nuclear Collection of Brassica oleracea L. Landraces to Grow at High Temperatures

Statistical models predict that global warming will have a negative impact in crop yields in the next decades. Especially vulnerable are winter crops such as kales or cabbages (Brassica oleracea L.). We evaluated the impact of high temperatures in morphological and biochemical traits of a B. oleracea core collection during early development. When grown at 30 °C, plants showed a reduction in chlorophyll content, early vigour and biomass compared with values observed on plants grown at 20 °C. Likewise, the total content of glucosinolates shows a reduction at high temperatures. The alboglabra group showed the best general performance at 30 °C for both morphological traits and glucosinolate content. Based on a cluster analysis, we selected four populations (MBG0072, MBG0464, MBG0535 and HRIGRU5555) as the most promising to be used in further breeding programs for heat tolerance.     

Glucosinolates and Resistance to Leptosphaeria maculans in Wild and Cultivated Brassica Species

Synthetic lines of Brassica napus were derived by combining the genomes of B. atlantica and B. oleracea var. alboglabra, which were respectively resistant and susceptible to foliar infection by Leptosphaeria maculans, with a susceptible line of B. rapa. Resistance was expressed in the synthetic lines containing the genome of B. atlantica. The high levels of alkenyl glucosinolates which occur in leaves of B. atlantica, and which have been implicated in disease resistance, were also expressed within the synthetic lines, although the dominant glucosinolate had changed from sinigrin to glucobrassicanapin. Disease resistance and glucosinolate profiles did not co-segregate in F₂ progeny from crosses between the synthetic lines.     

Screening for resistance to black rot in a Spanish collection of Brassica rapa

Productivity and quality of crops of Brassica rapa L. in north‐western of Spain are highly affected by black rot, caused by the bacterium Xanthomonas campestris pv. campestris (Pammel) Dowson (Xcc). Several races of Xcc have been described in this area, being the race 6 the most frequent in B. rapa crops and races 1 and 4 the most frequent in B. oleracea crops. The control of the disease can be aided by the employment of resistant varieties. The aim of this work was to find sources of resistance to Xcc in a collection of open‐pollinated varieties of B. rapa from north‐western Spain. Resistance was evaluated in 191 landraces. Partial resistance to races 6, 1 and 4 and complete resistance to race 4 were identified in several landraces. Several accessions exhibited partial resistance to the three races. Sources of resistance were identified in landraces of different crops of the species (turnips, turnip greens and turnip tops). These landraces could be grown after selection for resistance or they can be donors of resistance genes in breeding programmes.     

Maternal Effects on the Expression of Individual Aliphatic Glucosinolates in Seeds and Seedlings of Brassica napus

An investigation into the glucosinolate profile of seed and leaf tissue of F₁ hybrids from reciprocal crosses between B. napus‘Cobra’ and a synthetic B. napus line was undertaken to test hypotheses concerning the site of biosynthesis of seed glucosilates. The profile of the seed aliphatic glucosinolates was dentical to the maternal parent suggesting the absence of glucosinolate biosynthesis and glucosinolate interconversion within the embryo and the transfer of fully formed glucosinolates from maternal tissue into the developing seed. In cotyledons, while there was no evidence for de novo glucosinolate biosynthesis, there was evidence for side chain modication and the interconversion of existing glucosinolates. in true leaves, the glucosinolate profile of the reciprocal F₁ hybrids were identical, and in accordance with that expected from the F₁ genotype.     

Detection of loci controlling seed glucosinolate content and their association with Sclerotinia resistance in Brassica napus

A genetic linkage map of Brassica napus constructed from a cross between a low glucosinolate cultivar ‘H5200’ and a high glucosinolate line ‘NingRS‐1’ was used to identify loci associated with seed glucosinolate content and to understand the association between specific glucosinolate components and Sclerotinia resistance. Seed glucosinolate content was assessed by standard High pressure Liquid Chromatogram (HPLC) protocol. Seven components of seed glucosinolate, including four types of aliphatic glucosinolate, two types of indolyl glucosinolates and one aromatic glucosinolate were detected in the seeds. Three quantitative trait loci (QTLs) were identified for seed total glucosinolate content. From three to 15 loci were found to be responsible for different types of glucosinolates, and by comparing the overlapped intervals, eight genomic regions were defined. One of the nine loci associated with aliphatic glucosinolate content was found to be associated with Sclerotinia resistance on the leaf at the seedling stage, and one locus, responsible for 3‐indolyl‐methyl glucosinolate content, was probably linked with Sclerotinia resistance on the stem of the maturing plant. The association between seed glucosinolate content and Sclerotinia resistance is discussed.     

Variation of glucosinolates and nutritional value in nabicol (Brassica napus pabularia group)

Glucosinolate levels in leaves were determined in a collection of 36 varieties of nabicol (Brassica napus pabularia group) from northwestern Spain grown at two locations. Crude protein, acid detergent fibre, and sensory traits were also assessed by a consumer panel. The objectives were to determine the diversity among varieties in total glucosinolate content and glucosinolate profile and to evaluate their sensory attributes in relation to glucosinolate content for breeding purposes. Eight glucosinolates were identified, being the aliphatic glucosinolates, glucobrassicanapin, progoitrin, and gluconapin the most abundant. Glucosinolate composition varied between locations although the glucosinolate pattern was not significantly influenced. Differences in total glucosinolate content, glucosinolate profile, protein, acid detergent fibre, and flavour were found among varieties. The total glucosinolate content ranged from 1.4 μmol g⁻¹ to 41.0 μmol g⁻¹ dw at one location and from 1.2 μmol g⁻¹ to 7.6 μmol g⁻¹ dw at the other location. Sensory analysis comparing bitterness and flavour with variation in glucosinolate, gluconapin, progoitrin, and glucobrassicanapin concentrations suggested that other phytochemicals are probably involved on the characteristic flavour. The variety MBG-BRS0035 had high total glucosinolate, glucobrassicanapin, and gluconapin contents at both locations and could be included in breeding programs to improve the nutritional value of this vegetable crop.     

Genetic and environmental effects on glucosinolate content and chemoprotective potency of broccoli

Broccoli is well recognized as a source of glucosinolates and their isothiocyanate breakdown products. Glucoraphanin is one of the most abundant glucosinolates present in broccoli and its cognate isothiocyanate is sulphoraphane, a potent inducer of mammalian detoxication (phase 2) enzyme activity and anti‐cancer agent. This study was designed to measure: glucosinolate levels in broccoli florets from an array of genotypes grown in several environments; the elevation of a key phase 2 enzyme, quinone reductase, in mammalian cells exposed to floret extracts; and total broccoli head content. There were significant environmental and genotype‐by‐environment effects on levels of glucoraphanin and quinone reductase induction potential of broccoli heads; however, the effect of genotype was greater than that of environmental factors. The relative rankings among genotypes for glucoraphanin and quinone reductase induction potential changed, when expressed on a per head basis, rather than on a concentration basis. Correlations of trait means in one environment vs. means from a second were stronger for glucoraphanin and quinone reductase induction potential on a per head basis than on a fresh weight concentration basis. Results of this study indicate that development of a broccoli phenotype with a dense head and a high concentration of glucoraphanin to deliver maximum chemoprotective potential (high enzyme induction potential/glucoraphanin content) is a feasible goal.     

The Inheritance of Aliphatic Glucosinolates in Brassica napus

The inheritance of aliphatic glucosinolates was studied in crosses between synthetic B. napus lines and oilseed rape cultivars. Six unlinked loci are described which determine the aliphatic glucosinolate profile of B. napus. One locus regulates the presence or absence of propyl glucosinolates, while another regulates the expression of pentyl glucosinolates. Two loci regulate the removal of the terminal H₃CS-group from the amino acid derivative to produce alkenyl glucosinolates as opposed to methylthioalkyl and methylsulphinylalkyl glucosinolates, regardless of the length of the alkyl chain. Likewise, another two loci regulate the hydroxylation of both butenyl and pentenyl glucosinolates. The functional alleles at one of the hydroxylation loci results in significantly more hydroxylation than those at the other locus. The large number of aliphatic glucosinolates which have been described in Brassica thus results from an interaction between genes which regulate side chain elongation and genes which modify the structure of the side chain, regardless of its length. The implications of this study for the biosynthesis of aliphatic glucosinolates, the origin of B. napus and the potential to manipulate the leaf and seed glucosinolate profile of oilseed rape are discussed.     

Leaf glucosinolate profiles and their relationship to pest and disease resistance in oilseed rape

Summary Glucosinolates are sulphur-containing glycosides which occur within vegetative and reproductive tissue of oilseed rape. Following tissue damage, glucosinolates undergo hydrolysis catalysed by the enzyme myrosinase to produce a complex array of products which include volatile isothiocyanates and several compounds with goitrogenic activity. Many of these products have been implicated in the interaction betweenBrassica and their pests and pathogens and some may have a role in defence mechanisms. Low glucosinolate (00) oilseed rape cultivars have been shown to possess similar concentrations of leaf glucosinolates as high glucosinolate (0) oilseed rape cultivars. Likewise, despite considerable speculation to the contrary, 00 cultivars have been shown not to be more susceptible to pests and pathogens than 0 cultivars. The potential to enhance pest and disease resistance of oilseed rape by manipulating the leaf glucosinolate profile without reducing seed quality is discussed.     

Production of a desirable Brassica oleracea CMS line using an alloplasmic B. rapa CMS line carrying Diplotaxis erucoides cytoplasm as a bridge plant

In Brassica oleracea, production of F₁ hybrid seeds mainly makes use of the improved Ogura cytoplasmic male sterile (CMS) line. However, reliance on one particular line is a risk, and it would be advantageous to develop other CMS lines. In this study, we transferred Diplotaxis erucoides cytoplasm to B. oleracea cultivars using an alloplasmic B. rapaCMS line as a bridge plant to avoid incompatibility between donor and recipient plants. The new B. oleraceaCMS lines, which were derived by four generations of backcrossing, had small rudimentary anthers with no pollen grain and showed complete male sterility. There was no functional defect in other floral organs, and the ability to receive normal pollen did not appear to be impaired. Moreover, the B. oleraceaCMS lines carrying D. erucoides cytoplasm had larger leaf areas and a normal plastochron. As a consequence, the B. oleraceaCMS lines carrying D. erucoides cytoplasm have the potential to be valuable alternatives for use in commercial B. oleracea hybrid seed production.     

Glucoraphanin and flavonoid levels remain stable during simulated transport and marketing of broccoli (Brassica oleracea var. italica) heads

Fresh broccoli heads contain relatively high levels of beneficial phytochemicals, particularly glucosinolates and flavonoids, but it is not clear whether or not the levels are affected by postharvest handling conditions. Accordingly, broccoli heads (Brassica oleracea var. italica) were stored at temperatures of 1 or 4 °C, 99% relative humidity (RH), for 2, 7, 14 or 28 days to simulate domestic and export transport conditions. After removal from cool storage, heads were then placed at 8, 15 or 20 °C, with 99, 90 or 70% RH, respectively, for 3 days to simulate marketing conditions. At the end of both phases, heads were rated for visual quality, turgor, presence of rots and yellowing, and the contents of glucoraphanin, quercetin and kaempferol were measured. Visual quality declined significantly with increasing temperature and length of storage, caused primarily by increasing yellowing and loss of turgor. Glucoraphanin, quercetin and kaempferol contents were not significantly affected by storage and marketing temperature and time. These results suggest that current transport and marketing practices are not likely to have a deleterious effect on the levels of aliphatic glucosinolates and flavonols in broccoli.     

Combination of resistance to Verticillium longisporum from zero erucic acid Brassica oleracea and oilseed Brassica rapa genotypes in resynthesized rapeseed (Brassica napus) lines

Resynthesized (RS) forms of rapeseed (Brassica napus L.; genome AACC, 2n = 38) generated from interspecific hybridization between suitable genotypes of its diploid progenitors Brassica rapa L. (syn. campestris; genome AA, 2n = 20) and Brassica oleracea L. (CC, 2n = 18) represent a potentially useful resource to introduce resistance against the fungal pathogen Verticillium longisporum into the gene pool of oilseed rape. Numerous cabbage (B. oleracea) accessions are known with resistance to V. longisporum; however, B. oleracea generally has high levels of erucic acid and glucosinolates in the seed, which reduces the suitability of resulting RS rapeseed lines for oilseed rape breeding. In this study resistance against V. longisporum was identified in the cabbage accession Kashirka 202 (B. oleracea convar. capitata), a zero erucic acid mutant, and RS rapeseed lines were generated by crossing the resistant genotype with two spring turnip rape accessions (B. rapa ssp. olerifera) with zero erucic acid. One of the resulting zero erucic acid RS rapeseed lines was found to have a high level of resistance to V. longisporum compared with both parental accessions and with B. napus controls. A number of other zero erucic acid RS lines showed resistance levels comparable to the parental accessions. In the most resistant RS lines the resistance and zero erucic acid traits were combined with variable seed glucosinolate contents. Erucic acid‐free RS rapeseed with moderate seed glucosinolate content represents an ideal basic material for introgression of quantitative V. longisporum resistance derived from B. oleracea and B. rapa into elite oilseed rape breeding lines.     

Seed Shattering of Cañahua (Chenopodium pallidicaule Aellen)

Cañahua (Chenopodium pallidicaule Aellen) is a semi‐domesticated relative of quinoa (Chenopodium quinoa Willd.) with high nutritious quality. It is tolerant to frost, drought, saline soils and pests. One seed yield limitation is seed loss during the maturity stages. Two greenhouse experiments in Denmark and field experiments in Bolivia were carried out to determine seed shattering in landraces and cultivars with different growth habits. 15–21 % of the seed shattering in the fields took place whilst the plants still were flowering and 25–35 % during physiological maturity. Seed shattering varied between locations on the Bolivian Altiplano. Cañahua types with the semi‐prostrate growth (‘lasta’) had the highest seed shattering rate in the greenhouse experiments. The Umacutama landrace had lower seed shattering (1 %) than the cultivar Kullaca (7.2 %) both of the ‘lasta’ type. Under field conditions, the cultivar Illimani with the erect growth (‘saihua’) had the highest seed shattering rate (6.4–33.7 %) at both locations and at four different sowing dates. The Umacutama had the lowest rate (0.5–1.5 %). There were no significant differences between plants of the ‘lasta’ and the ‘saihua’ types. The landrace had significantly less seed loss than the cultivars. However, in the greenhouse, the landrace yield was approximately 25 % lower than the yields of the cultivars. In general, cañahua cultivars had higher yield compared to landraces, but also a higher seed shattering rate. Landraces may be used in breeding programmes to develop high‐yielding cultivars with reduced seed shattering.     

Development and characterisation of a <Emphasis Type="Italic">Brassica carinata</Emphasis> inbred line incorporating genes for low glucosinolate content from <Emphasis Type="Italic">B. juncea</Emphasis>

The presence of high levels of sinigrin in the seeds represents a serious constraint for the commercial utilisation of Ethiopian mustard (Brassica carinata A. Braun) meal. The objective of this research was the introgression of genes for low glucosinolate content from B. juncea into B. carinata. BC₁F₁ seed from crosses between double zero B. juncea line Heera and B. carinata line N2-142 was produced. Simultaneous selection for B. carinata phenotype and low glucosinolate content was conducted from BC₁F₂ to BC₁F₄ plant generations. Forty-three BC₁F₄ derived lines were selected and subject to a detailed phenotypic and molecular evaluation to identify lines with low glucosinolate content and genetic proximity to B. carinata. Sixteen phenotypic traits and 80 SSR markers were used. Eight BC₁F₄ derived lines were very close to N2-142 both at the phenotypic and molecular level. Three of them, with average glucosinolate contents from 52 to 61 micromoles g⁻¹, compared to 35 micromoles g⁻¹ for Heera and 86 micromoles g⁻¹ for N2-142, were selected and evaluated in two additional environments, resulting in average glucosinolate contents from 43 to 56 micromoles g⁻¹, compared to 29 micromoles g⁻¹ for Heera and 84 micromoles g⁻¹ for N2-142. The best line (BCH-1773), with a glucosinolate profile made up of sinigrin (>95%) and a chromosome number of 2n = 34, was further evaluated in two environments (field and pots in open-air conditions). Average glucosinolate contents over the four environments included in this research were 42, 31 and 74 micromoles g⁻¹ for BCH-1773, Heera and N2-142, respectively. These are the lowest stable levels of glucosinolates reported so far in B. carinata.     

Genetic diversity in blast resistance of Bhutan rice landraces

With an objective to evaluate the Bhutan rice (Oryza sativa L.) landraces for genetic diversity in blast resistance, 402 accessions viz. 352 landraces, a differential set of 32 R gene lines and 18 modern cultivars were field-evaluated in three blast ‘hotspot’ sites followed by genetic analysis of the 352 landraces with 27 microsatellite markers. Across the sites, 19 landraces (5.4%) exhibited complete resistance with zero disease score and 203 (58%) and 163 (46%) landraces showed high partial resistance for early leaf and panicle blast, respectively, with disease score of four to six. Field evaluation for leaf and panicle blast at three experimental sites in Bhutan showed best cultivar discrimination in early leaf blast at the tillering stage (heritability, h² = 0.32) and in the panicle blast at maturity (h² = 0.44). Subdivision of the genetic variation into cultivar groups revealed the most variation for blast severity within the 352 landraces with h² of 0.31 and 0.46 for early leaf and panicle blast, respectively. Cluster analysis of the landraces revealed two distinct rice cultivar groups, which separated at dissimilarity of 0.84 according to origin of the cultivars from low, mid and high altitude zones in Bhutan. All microsatellites were polymorphic with two to 21 different alleles per marker and a high polymorphic information content value of 0.61. The identified blast resistant landraces were genetically diverse originating from different rice cultivation zones. Further investigation of the resistant and partial resistant material may reveal specific blast resistance genes, which could be useful to mitigate blast incidence in rice-producing countries.     

Genetic analysis of total glucosinolate in crosses involving a high glucosinolate Indian variety and a low glucosinolate line of Brassica juncea

Analysis of the glucosinolate content and composition by high‐pressure liquid chromatography indicated that varieties of Brassica juncea bred and grown in India have a high glucosinolate content characterized by the presence of 2‐propenyl (allyl) and 3‐butenyl as the major and 4‐pentenyl as the minor fractions. In contrast, the B. juncea germplasm from other countries is characterized by the presence of 2‐propenyl as the major glucosinolate fraction, trace amounts of 3‐butenyl and a total lack of the 4‐pentenyl types. In order to transfer the low glucosinolate trait to Indian B. juncea, the inheritance of total glucosinolates was investigated using doubled haploid (DH) populations derived from F1 (DH₁) and BC₁ (BC₁DH) of a cross between ‘Varuna’ (the most widely cultivated high glucosinolate variety of India) and ‘Heera’ (a non‐allyl type low glucosinolate line). A total of 752 DH₁ and 1263 BC₁DH gave rise to seven and 11 low glucosinolate (containing less than 18 μmol/g seed) individuals, respectively. On the basis of the frequency of the low glucosinolate individuals, the total glucosinolate was found to be under the control of seven genes. There was presence of both allyl and non‐allyl types in DH₁ and BC₁DH low‐glucosinolate individuals and absence of 3‐butenyl glucosinolate in some of the BC1DH low glucosinolate individuals, indicating segregation for these fractions in the population. The size of the segregating DH population proved to be crucial for precise determination of the number of genes controlling the trait. Because of the large number of genes involved, incorporation of low glucosinolate trait in Indian B. juncea should be approached through doubled haploid (DH) breeding.     

Alkenyl Glucosinolate Levels in Androgenic Populations of Brassica napus

The levels of individual and total alkenyl glucosinolates in seeds of microspore-derived spontaneous diploid plants from low by high and low by low glucosinolate parent crosses were examined to assess the utility of haploidy in canola breeding. The distributions of lines in the populations supported previous proposals that alkenyl glucosinolate levels are under multigenic control. Levels of all of the individual glucosinolates were positively correlated and were significantly reduced in canola-quality material in comparison to rapeseed-quality material. The populations of microspore-derived lines from low × high crosses were skewed to high glucosinolate levels but the population from a low × low glucosinolate cross had a greater proportion of low glucosinolate lines. The former observations can be explained in terms of the dominance of genes for high glucosinolate levels in Brassica napus. The present findings contradict previous reports that androgenic lines have higher glucosinolate content than the parents and in fact, haploidy may select for low glucosinolate lines when crosses between low glucosinolate parents are used.