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The coat protein (CP) gene of Tobacco streak virus (TSV) from sunflower (Helianthus annuus L.) was amplified, cloned and sequenced. A 421 bp fragment of the TSV coat protein gene was amplified and a gene construct encoding the hairpin RNA (hpRNA) of the TSV-CP sequence was made in the plasmid pHANNIBAL. The construct contains sense and antisense CP sequences flanking a 742 bp spacer sequence (Pdk intron) under the control of the constitutive CaMV35S promoter. A 3.6 kb Not I fragment containing the hpRNA cassette (TSV-CP) was isolated from pHANNIBAL and sub-cloned into the binary vector pART27. This chimeric gene construct was then mobilized into Agrobacterium tumefaciens strain LBA4404 via triparental mating using pRK2013 as a helper. Sunflower (cv. Co 4) and tobacco (cv. Petit Havana) plants were transformed with A. tumefaciens strain LBA4404 harbouring the hpRNA cassette and in vitro selection was performed with kanamycin. The integration of the transgene into the genome of the transgenic lines was confirmed by PCR analysis. Infectivity assays with TSV by mechanical sap inoculation demonstrated that both the sunflower and tobacco transgenic lines exhibited resistance to TSV infection and accumulated lower levels of TSV compared with non-transformed controls.

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Induction of systemic resistance to bacterial blight caused by Xanthomonas campestris pv. malvacearum in cotton by leaf extract from a medicinal plant zimmu (Allium sativum L. 6 Allium cepa L.) Abstract Aqueous extract (10%) from leaves of zimmu (Allium sativum L. 6 Allium cepa L.) when applied as foliar spray to first and second leaves of cotton plants induced systemic resistance in third and fourth leaves to a challenge infection with Xanthomonas campestris pv. malvacearum and reduced the number of lesions by up to 73% compared with water-treated control plants. The treated leaves exhibited significantly high activity of enzymes phenylalanine ammonia-lyase, peroxidase and polyphenol oxidase along with rapid accumulation of phenolics. The activities of chitinase and b-1,3-glucanase were greatly elevated in treated plants as compared to water-treated controls. An 11-fold increase in chitinase activity was evident 4 d after treatment. Western blot analysis revealed that a chitinase with an apparent molecular weight of 58 kDa that cross-reacted with a barley chitinase antiserum was induced in cotton leaves 3 d after treatment and the maximum induction of this chitinase was detected 4 d after treatment. The present study provides evidence for the induction of biochemical defence mechanisms in cotton leaves after treatment with leaf extract from zimmu.

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