A worldwide collection of Fusarium oxysporum f. sp. cubense was analyzed using anonymous, single-copy, restriction fragment length polymorphism (RFLP) loci. Several lines of evidence indicated that this pathogen has a clonal population structure. Of the 165 isolates examined, only 72 RFLP haplotypes were identified, and nearly half the isolates were represented by the five most common haplotypes. Individuals with identical haplotypes were geographically dispersed, and clone-corrected tests of gametic disequilibrium indicated significant nonrandom association among pairs of alleles for 34 of 36 loci tested. Parsimony analysis divided haplotypes into two major branches (bootstrap value = 99%) that together contained eight clades supported by significant bootstrap values. With the exception of two isolates, all isolates within a vegetative compatibility group were in the same clade and clonal lineage. Clonal lineages were defined by isolates having coefficients of similarity between 0.94 and 1.00. Ten clonal lineages were identified, and the two largest lineages had pantropical distribution. Minor lineages were found only in limited geographical regions. Isolates composing one lineage (FOC VII) may represent either an ancient genetic exchange between individuals in the two largest lineages or an ancestral group. The two largest lineages (FOC I and FOC II) and a lineage from East Africa (FOC V) are genetically distinct; each may have acquired the ability to be pathogenic on banana independently.

Cost-effective, laborsaving, and environmentally sound weed management practices are needed for sustainable vegetable production. Organic production, in particular, precludes the use of synthetic herbicides and requires that organic farmers utilize practices that reduce harmful environmental impact. Although polyethylene film mulch is used extensively in vegetable production in Florida, its use has a number of drawbacks, among which is the susceptibility of opaque polyethylene mulch to penetration by yellow and purple nutsedge. Appreciable labor and disposal/environmental costs are associated with its removal. A durable mulch material that would effectively control nutsedge and other weeds but with no associated environmental and disposal costs is highly desirable. Hydramulch, a paper-like material applied as a slurry consisting of cotton waste, newsprint, gypsum and a proprietary adhesive, was tested as a biodegradable alternative to polyethylene mulch during the spring of 2003. Experiments were conducted in southeastern and north-central Florida to compare the effects of three hydramulch formulations, polyethylene mulch and a no mulch control on soil temperature, soil moisture and weed infestation. Soil temperature under hydramulch was 1–4°C lower than that under polyethylene. In the absence of rain, the use of hydramulch resulted in soil moisture levels that were 1–4% lower than with polyethylene mulch. Higher soil moisture with hydramulch than polyethylene was coincident with rainfall. Hydramulch remained intact on most beds and suppressed broadleaf weeds and grasses, particularly at the north-central site where the mulch was applied at a greater thickness. However, purple nutsedge readily penetrated hydramulch. Therefore, hydramulch may be applicable for use for the suppression of broadleaf weeds and grasses at sites with little or no nutsedge pressure in fall or in crops for which cooler soils are desirable or crops that are rainfed or overhead irrigated.

Additional index words. sunn hemp, Crotalaria juncea, cover crop, cultural weed management Abstract. A field study was conducted in 2008 and 2009 in Citra, FL, to evaluate the effects of seeding rate and removal of apical dominance of sunn hemp (Crotalaria juncea L.) on weed suppression and seed production by sunn hemp. Three seeding rates of sunn hemp were used: a representative seed production rate of 11 kg · ha L1 , an intermediate seeding rate of 28 kg · ha L1 , and a cover crop seeding rate of 45 kg · ha L1 . Cutting the main stem at 3, 4, or 5 weeks after planting to break apical dominance was compared with an uncut treatment. Cutting had no significant effect on shoot biomass, photosynthetically active radiation (PAR) penetrating the canopy, and nondestructive leaf area index (LAI). As a result, cutting also had no effect on weed density and biomass in 2008 and very little effect in 2009. Increase in seeding rate resulted in linear decrease in PAR and increase in LAI in both years. Seeding rate had a greater effect on suppression of weed biomass than on suppression of weed density. There was a linear decline in sunn hemp branching with increased seeding rate in 2009 and, averaged across years, flower number decreased linearly with increased seeding rate. Cutting to break apical dominance induced branching but had no effect on flower number. No seed pod production occurred and we postulate that the lack of seed production may be the result of the absence of effective pollinators in fall when short-day varieties of sunn hemp flower in Florida.

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Adoption of sunn hemp (Crotalaria juncea L.) as a cover crop has been limited primarily due to the availability of seed sources, leading to high seed costs and unreliable supplies. Seed production in Florida with the commercially available sunn hemp cultivar Tropic Sun has been largely unsuccessful. An experiment was designed to evaluate 16 accessions of sunn hemp for potential commercial seed production in Florida at three planting dates (May, June, July). Vegetative and reproductive characteristics were evaluated to provide baseline information for future development of a cultivar of sunn hemp that could produce seed in Florida with desirable cover crop attributes. The results indicate that the sunn hemp accessions could be separated into two groups. Regardless of planting date, accessions in Group 1 (PI 234771, PI 248491, PI 295851, PI 337080, PI 468956, PI 561720, PI 652939) displayed desirable cover crop characteristics, such as high biomass production and leaf area. Accessions in Group 1 had a short‐day flowering response and produced few to no pods and seeds. Group 2 accessions (PI 207657, PI 250485, PI 250486, PI 250487, PI 314239, PI 322377, PI 346297, PI 391567, PI 426626) were less sensitive to photoperiod, were generally smaller plants because of earlier transition to reproductive growth, and produced more seedpods and seeds. Seed production was generally better when seeds were sown at the earliest date. It appears that in Florida, sunn hemp accessions that are capable of flowering in summer rather than fall have greater potential for seed production.Core Ideas Based on vegetative and reproductive characteristics sunn hemp accessions could be divided into two groups. Group 1 accessions produce more shoot biomass and have a short‐day flowering response. Flowering occurs in fall when effective pollinators are absent. Group 2 accessions are less sensitive to photoperiod. Group 2 accessions flower in summer when effective pollinators occur and successfully set seed.