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 H3CSgroup 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 glucosinoiates, the origin of B. napus and the potential to manipulate the leaf and seed glucosinolate profile of oilseed rape are discussed.

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Citrus tristeza virus (CTV) isolates collected from the Lower Rio Grande Valley in south Texas and east Texas were characterized using citrus indicators and molecular methods. The citrus indicators were Mexican lime (Citrus aurantifolia), sour orange (C. aurantium), sweet orange (C. sinensis) grafted to sour orange, Duncan grapefruit (C. × paradisi), and Madam Vinous sweet orange, with some CTV isolates additionally indexed using the Texas commercial grapefruit cvs. Rio Red and Star Ruby, and Marrs and N-33 sweet orange. Severity ratings used 11 biotype groups or cumulative mean relative indices. Molecular characterization was carried out using poly- and monoclonal antibodies, seven strain-specific probes and single-stranded conformational polymorphism, and all were based on the CTV major coat protein or gene. All Texas CTV isolates produced vein clearing symptoms on inoculated Mexican lime plants. Over half of the CTV isolates tested were placed in biotype groups IX and X (causing decline of sweet orange on sour orange, seedling yellows on sour orange and grapefruit seedlings, and stem pitting of grapefruit or sweet orange), and one isolate was in biotype I (mild).

Twenty-five citrus samples from 16 sites in the Lower Rio Grande Valley and Corpus Christi areas of Texas were indexed for Citrus tatter leaf virus (CTLV). Sixteen samples gave characteristic CTLV symptoms when biologically indexed onto citrumelo or citrange indicators. Six of the samples could also be readily detected by ELISA using the original donor tissue with CTLV and Apple stem grooving virus (ASGV) ELISA. No tissue samples reacted with Citrus tristeza virus antibodies. Indexing on limited herbaceous indicators proved unreliable under our conditions. Four of the samples with distinct CTLV symptoms gave bud union browning on citrange as early as 12 mo after grafting. Five samples were further indexed on a range of citrus indicators in 1997, the type and extent of symptoms observed are described.

and Tanga regions of the Tanzania mainland, and Unguja and Pemba islands of Zanzibar. The samples were tested using replicated DAS-I ELISA with Florida Citrus tristeza virus (CTV) antibodies (CREC28/G604). The tissues tested were either fresh or dried leaf midribs from near mature leaves. Most mature trees were observed as poorly productive with thin canopies. All mature Mexican lime seedlings that had observable stem-pitting CTV symptoms under a bark flap were positive by ELISA. Most, (97%), of the samples collected in the Bagamoyo district (Coastal region) and Kinondoni district (Dar-es-Salaam region) were CTV positive. Over all tests, 65% of samples were CTV-infected. Only one infestation of aphids was observed and a sample of these aphids was later confirmed as Toxoptera citricida Kirkaldy.