Mango explant browning: Effect of ontogenic age,mycorrhization and pre-treatments

The in vitro performance of mango shoot culture is delimited by several factors, of which explant necrosis and media browning are considered as major constraints for successful exploitation of such an important commercial crop. Our results showed that source of explants had a significant effect on the performance of in vitro cultures of mango. The variations in survival of explants collected from glasshouse grown seedlings and field-grown stock plants indicated towards differences between their physiological/ontogenic age. Though, chronologically, both are young, the glasshouse grown shoots are ontogenetically younger and; therefore, responded better over field-grown shoots. Improved performance of explants harvested from mycorrhizal plants suggests integration of mycorrhizal biotechnology with tissue culture biotechnology in order to achieve better results as mycorrhiza being a well-known stress alleviator may help explants mitigate in vitro stresses. Furthermore, shoot tip explants of field-grown ‘Amrapali’ mango was assayed for their browning propensity at pre- and post-culture stages. Status of different bio-chemicals such as in vivo phenol, in vitro phenol exudation, phenylalanine ammonia lyase, peroxidase and polyphenol oxidase as affected by various pre-treatments were estimated to establish the relationship of these bio-chemicals with necrosis of mango shoot cultures. The different pre-treatments comprised etiolation of newly emerged shoots (5–7 days old) of stock plants using black polythene for 7 days, etiolation treatment + agitation of explants in antioxidant solution (antioxidants: ascorbic acid at 100 mg l⁻¹ + citric acid at 50 mg l⁻¹), etiolation treatment + agitation of explants in polyvinylpyrrolidone solution (PVP) at 0.2% and non-etiolated control. Of these, explants treated with PVP proved to be superior to other treatments with regards to explant necrosis percentage as such explants exhibited least activities of phenols and oxidative enzymes. Correlation studies indicated existence of high positive correlation between explant necrosis and these bio-chemicals.     

Characterization of Fusarium population associated with wilt of jojoba in Israel

Fusarium wilt, caused by Fusarium oxysporum, is a major disease of jojoba, causing serious economic losses. This study was aimed at characterizing the Fusarium populations associated with jojoba in Israel. Fifty Fusarium isolates used in this study included 23 isolates from the 1990s (“past”) and 27 recently isolated (“recent”). All the isolates were characterized by arbitrarily primed (ap)-PCR and 16 representatives were additionally delineated using multilocus (tef1, rpb1, rpb2) phylogeny and evaluated for their pathogenic potential. Consequently, 88% of the isolates were identified and characterized to the F. oxysporum species complex. The remaining 12% grouped within the F. fujikuroi, F. solani, and F. redolens species complexes. Variations in the infection rate (16.7%–100%), disease symptoms (0.08–1.25, on a scale of 0–3), and fungal colonization index (0.67–2.17, on a scale of 0–4) were observed within the tested isolates, with no significant differences between the past and recent isolates. The representative isolates were assigned to 11 groups based on ap-PCR. Pathogenicity tests showed that isolates from Groups II, IV, and V were the most aggressive, whereas isolates from Groups III, VIII, and IX were the least aggressive. Among the tested isolates, F. oxysporum sensu lato was the most aggressive, followed by F. proliferatum, while F. nygamai was the least aggressive. This study demonstrates the complexity and genetic diversity of Fusarium wilt on jojoba in Israel, indicating possible multiple introductions of infected germplasm into the country.     

Non-structural protein 3A for differentiation of foot-and-mouth disease infected and vaccinated animals in Haryana (India)

There are severe international trade restrictions on foot-and-mouth disease (FMD) affected areas. Because of endemic nature of FMD, India started FMD control programme (FMD-CP) using mass vaccination in selected states including Haryana (year 2003). Although no significant incidence of the disease was reported after launching FMD-CP in the state but in order to participate in international trade of animal and animal products, veterinary authorities have to prove that there is no FMD virus (FMDV) circulation in the animal population, for which it is necessary to differentiate the FMD infected and vaccinated animals. For this purpose, an in-house indirect ELISA utilizing baculovirus-expressed FMDV non-structural protein (NSP) 3A was used to find evidence for virus circulation (prevalence of anti-NSP 3A-specific antibodies) by examining serum samples that were collected either before start of FMD-CP or after completion of third phase (Pre-4th) of vaccination in Haryana (India). A significant reduction (P < 0.01) in prevalence of anti-NSP 3A-specific antibodies (possibly carriers) was observed 2 years after launching FMD-CP in Haryana. However, in cattle the percentage of animals with anti-NSP 3A-specific antibodies was found to be significantly higher (P < 0.01) than buffalo, both before (P < 0.01) and after (P < 0.01) launching FMD-CP in the state. The findings of this study suggest that use of FMDV vaccine in cattle and buffaloes in endemic areas reduces virus circulation (carriers) in the vaccinated herds and that the current 3ANSP-ELISA can be successfully used to monitor the FMDV circulation in endemic areas.     

Race-specific genetics of resistance to black rot disease [Xanthomonas campestris pv. campestris (Xcc) (Pammel) Dowson] and the development of three random amplified polymorphic DNA markers in cauliflower

Summary

In order to understand the genetics of resistance to black rot disease caused by Xanthomonas campestris pv. campestris (Xcc) (Pammel) Dowson in cauliflower (Brassica oleracea var. botrytis L.) and to identify random amplified polymorphic DNA (RAPD) markers that segregate with the resistance genes, susceptible (‘Pusa Himjyoti’, female parent) and resistant (‘BR-161’, pollen parent) plants were crossed. Six generations of plants (30 P₁, 30 P₂,30 F₁, 120 F₂, 90 B₁, and 90 B₂) were evaluated for the presence or absence of black rot disease in a randomised block design with three replications. The pattern of segregation of resistance was tested by the χ² test at the 5% level of significance. All F₁ progeny plants were resistant, and the segregation of resistant and susceptible plants in the F₂ and two backcross generations (B₁ and B₂) showed that a single dominant gene caused resistance to the black rot pathogen in ‘BR-161’. Three polymorphic RAPD markers (OPO-04₈₃₃, OPAW-20₂₅₃₈, and OPG-25₆₂₅) were found by bulk segregant analysis, which produced unique amplicons 833 bp, 2,538 bp, and 625 bp in length, respectively. These markers were associated in coupling phase to the resistance allele. Best fit ratios of 3:1 (resistant:susceptible) in the F₂ plants with the three RAPD markers, suggested that the markers were linked to the single gene controlling black rot resistance. These markers will be useful to identify more closely-linked markers and to develop black rot-resistant hybrid cauliflower varieties.     

Identification of soybean strains resistant to Xanthomonas campestris pv. glycines

Summary Soybean germplasm was screened for resistance to bacterial pustule disease. The etiological agent, Xanthomonas campestris pv. glycines, was isolated from the leaves of field grown soybean in Maharashtra, India. The screening of soybean stocks was carried out by excised leaf inoculation method. A differential susceptibility to the pathogen was observed in the tested stocks. Two stocks P-4-2 and P-169-3 were found to be completely resistant to the pathogen and displayed an incompatible reaction. Four cultivars, EC-34160, Bragg, Kalitur and PK-472 displayed moderate resistance and the remaining stocks were susceptible to the attack of the pathogen. The stocks P-4-2 and P-169-3 remained resistant even to a high concentration of 10⁹ colony forming units (cfu)/ml of the pathogen.     

Effect of cytoplasmic male-sterility in sorghum on host plant interaction with sorghum midge,Contarinia sorghicola

Summary Sorghum midge, Contarinia sorghicola Coq. (Diptera: Cecidomyiidae) is one of the most important pests of grain sorghum worldwide. We studied the reaction of midge-resistant and midge-susceptible genic-cytoplasmic male-sterile (A-lines) and their maintainers (B-lines), and the effect of resistant and susceptible restorers on sorghum midge. Midge damage and adult emergence were significantly lower on the B-lines of midge-resistant genotypes (PM 7061 and PM 7068) than their corresponding A-lines, while the reverse was true for the midge-susceptible genotypes (296A and ICSA 42). Differences in midge damage and the number of midges emerged were not significant between the midge-resistant and midge-susceptible A-lines when infested without pollination (except midge emergence on PM 7061A). Pollination with a midge-resistant restorer (DJ6541) reduced midge emergence significantly in one of two seasons. Source of pollen did not influence midge emergence on the highly-resistant A-line, PM 7061A. The implications of these observations in the development of midge-resistant hybrids were discussed.     

Discovery of a new gene causing dark green cotyledons and pathway of pigment synthesis in lentil (Lens culinaris Medik)

A new gene is reported which functions as a master gene for synthesis of the pigments determining cotyledon colour in lentil. This gene is different from the two earlier reported genes which are responsible for synthesis of yellow (gene Y) and brown (gene B) pigments. Double recessive homozygous condition of these two genes results into loss of both pigments and, consequently, produces light green cotyledons. The new gene, in contrast, produces dark green cotyledons in recessive condition irrespective of the dominance or recessive state of the Y and B genes. It is hypothesized that the new gene for dark green cotyledon colour (Dg) acts at an earlier stage in the biosynthesis of the two cotyledon-specific pigments, which are derived from a common precursor, whose synthesis is blocked when Dg mutates to its recessive condition. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inheritance and molecular mapping of restorer‐of‐fertility (Rf) gene in A2 hybrid system in pigeonpea (Cajanus cajan)

Inheritance of fertility restorer gene in pigeonpea was studied using F₂ and BC₁F₁ populations derived from cross AL103A × IC245273. It was found to be controlled by single dominant gene. Out of 228 SSR primer pairs, 33 primer pairs showed parental polymorphism, while four primers were found polymorphic in bulk segregant analysis (BSA). These four primers viz., CcM 1615, CcM 0710, CcM 0765 and CcM 1522 were used for genotyping of F₂ population and were found to be placed at 3.1, 5.1, 28.1 and 45.8 cM, respectively. Two of them, CcM 1615 and CcM 0710, evinced clear and unambiguous bands for fertility restoration in F₂ population. The Rf gene was mapped on linkage group 6 between the SSR markers CcM 1615 and CcM 0710 with the distances of 3.1 and 5.1 cM, respectively. The accuracy of the CcM 1615 was validated in 18 restorers and six maintainer lines. The marker CcM 1615 amplified in majority of male restorer lines with a selection accuracy of 91.66%.     

Variation in inheritance of resistance to sorghum midge, Stenodiplosis sorghicola across locations in India and Kenya

Sorghum midge [Stenodiplosis sorghicola (Coquillett)] is an important pest of grain sorghum, and host plant resistance is one of the important components for the management of this pest. We studied the inheritance of resistance to this insect involving a diverse array of midge-resistant and midge-susceptible genotypes in India and Kenya. Testers IS 15107, TAM 2566, and DJ 6514, which were highly resistant to sorghum midge in India, showed a greater susceptibility to this insect in Kenya. The maintainer lines ICSB 88019 and ICSB 88020 were highly resistant to sorghum midge in India, but showed a susceptible reaction in Kenya; while ICSB 42 was susceptible at both the locations. General combining ability (GCA) effects for susceptibility to sorghum midge for ICSA 88019 and ICSA 88020 were significant and negative in India, but such effects were non-significant in Kenya. The GCA effects of ICSB 42 for susceptibility to sorghum midge were significant and positive at both the locations. The GCA effects were significant and positive for Swarna, and such effects for IS 15107 and TAM 2566 were negative at both the locations. GCA effect of DJ 6514 were significant and negative in India, but non-significant and positive in Kenya; while those of AF 28 were significant and positive during the 1994 season in India, but significant and negative in Kenya. Inheritance of resistance to sorghum midge is largely governed by additive type of gene action. Testers showing resistance to sorghum midge in India and/or Kenya did not combine with ICSA 88019 and ICSA 88020 to produce midge-resistant hybrids in Kenya. Therefore, it is essential to transfer location specific resistance into both parents to produce midge-resistant hybrids.