Induction of Systemic Resistance to Albugo candida in Brassica juncea by Pre- or Coinoculation with an Incompatible Isolate

ABSTRACT In an investigation of the interaction between two isolates of Albugo candida that were compatible (CO) and incompatible (IN) on a Brassica juncea accession, the IN isolate induced both local and systemic protection of cotyledons and true leaves against the CO isolate. The extent of the protection was proportional to the zoosporangia concentration used in the inducing (IN) inoculation. Protection was greatest locally on cotyledons and least on true leaves (the most remote tissue from the point of the inducing inoculation). Protection occurred when the two isolates were inoculated together but was greater when the interval between the IN and CO isolate inoculations was longer. The IN isolate induced only slight protection when it was inoculated after the CO isolate. No induced susceptibility to the IN isolate occurred with any treatment. There was some evidence of competition between CO and IN zoospores for infection sites (stomata). The occurrence of systemic protection and changes detected in phenylalanine ammonia lyase and total soluble peroxidase activities in inoculated cotyledons, particularly after the inducing (IN) inoculation, suggested that host-mediated factors also may be involved in the interaction between the two isolates.     

Response of interspecific Brassica juncea/Brassica rapa hybrids and their advanced progenies to Albugo candida (white blister)

Transfer of factors for resistance to white blister disease caused by Albugo candida between Brassica species involving two genotypes each of B. juncea and B. rapa was studied in hybrids. More hybrids were obtained by in vivo than in vitro techniques, although an in vitro phase was a prerequisite for the establishment of in vivo hybrids. Hybrids were identified by PCR-based inter-simple sequence repeat (ISSR) markers with both male and female species-specific bands being identified. There was a positive correlation between disease severity and number of days after sowing ( r  > 0·93), the highest being towards pod formation and plant maturity at 110 days after sowing. The plants from F₂ and BC₁ progeny showed higher resistance to A. candida than either of the parents. Plants of B. juncea and B. rapa with high field resistance (disease index < 1·0) were selected from BC₂ and F₂BC₁ generations. The frequency of plants classified as resistant in BC₂ progeny ranged from 4·5 to 39·0% in cross-combinations involving B. juncea genotypes as female parent, compared with 100% in the reciprocal cross involving B. rapa as female parent.     

Pathological and biochemical changes in Brassica juncea (mustard) infected with Albugo candida (white rust)

Components of disease reaction, including incubation period, pustule types, inoculum production and disease index (DI); and contents of protein, phenols, soluble sugars and reducing and non-reducing sugars were investigated in cotyledonary and true leaves of six genotypes of Brassica juncea : Varuna, Kranti, EC-399296, EC-399299, EC-399313 and EC-399301, inoculated with Albugo candida . Cotyledonary leaves were examined 14 days after inoculation (d.a.i.), whereas true leaves were scored 14 and 21 d.a.i. Disease indices were assessed on a 0% (resistant) to 100% (susceptible) scale. DIs at the cotyledonary leaf stage in the above six genotypes were 67, 65, 32, 31, 31 and 38%, respectively, whereas at the true-leaf stage they were 21, 28, 12, 17, 9 and 4%, respectively at 14 d.a.i., and 35, 45, 17, 19, 20 and 6%, respectively at 21 d.a.i. Protein contents were highest in the genotypes with the highest DIs, such as Varuna at the cotyledonary leaf stage and Kranti at the true-leaf stage, and lowest in the genotypes with the lowest DIs, such as EC-399299 at the cotyledonary stage and EC-399301 at the true-leaf stage. Total phenols, total sugars, reducing sugars and non-reducing sugars were generally negatively correlated with DI, but were not always consistent, particularly when differences in DI were small. The results indicated that factors conditioning the response of host genotypes to A. candida may differ or operate in different ways at different growth stages.     

Inheritance of partial resistance to race 2 of Albugo candida in canola-quality mustard (Brassica juncea) and its role in resistance breeding

The inheritance of partial resistance to race 2 of Albugo candida was studied in a canola-quality line of Brassica juncea . This partially resistant line was crossed with the susceptible B. juncea cultivar Commercial Brown. F₁, F₁(reciprocal), F₂, BC and doubled haploid generations from the cross were inoculated with a zoospore suspension of race 2 to study segregation of partial resistance. The partially resistant phenotype appeared to be controlled by a single dominant gene that has variable expression. This partial resistance can have implications in breeding for disease resistance against white rust, as adult plants did not develop hypertrophic growth or stagheads under greenhouse and field conditions.     

Induction of Resistance in Mustard (Brassica juncea) against Alternaria Black Spot with an Avirulent Alternaria brassicae Isolate-D

Resistance in susceptible mustard cv. PR-15 against the highly virulent A. brassicae isolate A (AbA) and moderately virulent isolate C (AbC) was induced using an avirulent Alternaria brassicae isolate D (AbD). The induction of resistance due to AbD against AbA or AbC resulted in significant reduction in disease severity. The A. alternata (Aa) failed to induce resistance against AbA and AbC, on the contrary it induced susceptibility against them.     

Induction of resistance to downy mildew (Peronospora parasitica) in cauliflower by DL-β-amino-n-butanoic acid (BABA)

Of the three isomers of aminobutyric acid, only the β isomer (BABA) was effective in inducing resistance against Peronospora parasitica , the causal agent of downy mildew, in cauliflower ( Brassica oleracea var. botrytis ). A single foliar spray applied to 7-day-old seedlings protected the plants against Peronospora parasitica for at least 15 days. Of the enantiomers (R and S), only the R was effective. Resistance was accompanied by a hypersensitive-like reaction (necrotic spots) which was evident before inoculation. BABA was systemically effective when applied to the roots, but failed to protect cotyledons adjacent to treated ones. Unlike other chemical inducers, BABA was effective when applied several hours postinoculation. It had no effect on P. parasitica spore germination. In cauliflower seedlings, BABA did not induce the accumulation of the pathogenesis-related protein PR-1, PR-2, PR-3, PR-5 and PR-9. Only treated and challenged seedlings accumulated PR-2.