The genetic diversity of the U.S. Cucumis sativus L. germplasm collection [757 plant introductions (PI) representing 45 countries] was assessed using 40 enzymes which represented 74 biochemical loci. Polymorphisms were observed at 18 loci (G2dh-1, Gpi-1, Gpi-2, Gr-1, Gr-2, Idh, Mdh-1, Mdh-2, Mdh-3, Mpi-2, Pepla-2, Peppap-2, Per-4, Pgd-1, Pgd-2, Pgm-1, Pgm-3, and Skdh). Two PIs (285606 and 215589) contained alleles [G2dh-1(1) and Per-4(2), respectively] which did not occur in any other PI. Other alleles which occurred in low frequencies (in < 1% of the PIs) included Gpi-1(3), Gpi-2(3), Gr-1(3), Gr-2(1), Idh(1), Mdh-1(2), Mdh-2(1), Peppap-2(1), and Pgd-1(1). Individual loci containing more than one allele in greater than 20% of the PIs included Mpi-2, Pepla-2, Pgd-2, and Pgm-1. Multivariate analyses aided in the reduction of data (principle components), depicted relationships among PIs (cluster), and identified the most discriminating enzyme loci (Pgm-1, Pepla-2, Gr-1, Pgd-2, Mpi-2, and Skdh) (classification and regression tree).

Genetic analyses were conducted among 18 provisionary isozyme loci in Cucumis sativus L. Fourteen loci demonstrated simple Mendelian inheritance while observed variation at four loci (Gpi2, Gr2, Pgm3, Skdh2) was determined not to have a predictable genetic basis. Joint segregation analyses among the 14 genetically predictable polymorphic loci resulted in the assignment of 12 loci to four linkage groups. Linkage groups contain the following loci: (1) Gr1, Pgm1, Idh, Pgd1; (2) Pep-pap, Mdh2, Mdh3, Gpi1; (3) Pep-la, Per4; (4) Pgd2, G2dh. Mpi2 and Mdh1 segregated independently. Recombination fractions for linked loci ranged between 0.051 (Pgm1-Idh) to 0.385 (Pep-la-Per4). Some practical applications of isozyme marker loci for cucumer improvement are discussed.

Cotyledons of seven African species within Cucumis, subgenus Melo, subgroup Myriocarpus (4x C. aculeatus, C. anguria var. anguria Meeuse, C. dipsaceus Ehrenb. ex Spach, C. ficifolius A. Rich, C. myriocarpus ssp. leptodermis Schweik., C. prophetarum, and 2x and 4x C. zeyheri Sond.), and 2x C. sativus L. of subgenus Cucumis were surveyed using horizontal starch gel protein electrophoresis to characterize interspecific and intraspecific variation. Cluster and classification and regression tree analysis of allelic frequencies among 14 polymorphic loci indicated that C. myriocarpus ssp. leptodermis, C. prophetarum ssp. dissectus, C. ficifolius, C. anguria var. anguria, and 2x and 4x C. zeyheri have biochemical affinities and could be distinguished from C. aculeatus and C. dipsaceus, which were similar. Within the first group, C. myriocarpus ssp. leptodermis and C. prophetarum ssp. dissectus accession formed a well-defined group. Cucumis prophetarum ssp. dissectus was more similar to C. myriocarpus ssp. leptodermis than to the C. ficifolius accessions evaluated. In the second group, two C. zeyheri accessions (C81321, C80346) were more similar to C. prophetarum ssp. prophetarum (C82069) than four other C. zeyheri evaluated. Cucumis sativus was dissimilar from all other species studied. Key words: evolution, biochemical genetics, isozymes.

The growth and yield of three cucumber (Cucumis sativus L.) genotypes were evaluated in 1987 and 1988 using three planting arrangements and four weed control treatments. A monoecious, indeterminate, normal leaf cultivar, Calypso, a gynoecious, normal leaf size determinate × monoecious determinate F1 hybrid (UW 11234), and a gynoecious, determinate little leaf inbred line (WI 50476) were evaluated for fruit yield at a 30-cm equidistant (109,000 plants/ha), a 20-cm equidistant (242,000 plants/ha), and a 43-cm row (272,000 plants/ha) spacing. Weed control treatments consisted of an unweeded control, naptalam benzoic acid at 6.7 kg ae/ha, chloramben at 4.5 kg ae/ha, and the herbicides in combination. Although number and weight of fruit per hectare increased with increasing plant density, fruit weight per plant decreased with increasing density. Fruit harvested from plants in unweeded control plots were significantly smaller than those in herbicide-treated plots, and fruit yield of unweeded control plots was lower than in nonweedy plots in 1987. In 1987, plants in plots treated with naptalam produced smaller fruit than plants in plots treated with chloramben or chloramben plus naptalam. Although fruit yield per plant in 1987 was similar in chloramben plots with or without naptalam and generally higher than that of plots treated only with naptalam, fruit yields from naptalam-treated plants were highest in 1988. `Calypso' usually produced more and larger fruit than the determinate genotypes. Based on comparisons of fruit per plant under comparable spacings, productivity of WI 5047G was often lower and its fruit were smaller than those of normal leaf genotypes. Plants of WI 5047G may not attain the source capacity needed for adequate fruit growth before the onset of anthesis, thus producing smaller fruit. Chemical names used: (2-[(1-naphtalenylamino)carbonyl)benzoic acid (naptalam); 3-amino-2,5dichlorobenzoic acid (chloramben).

Naptalam at 6.7 kg ae/ha applied with chloramben at 2.0 to 4.5 kg ae/ha was a safener for chloramben phytotoxicity to cucumber as expressed by increased dry weight in the greenhouse and yield in the field, but the protection was inadequate to be commercially acceptable. Naptalam applied in seed coatings also protected cucumber from chloramben phytotoxicity in the greenhouse but were ineffective in the field. Delaying chloramben application 24 to 72 h after naptalam application in the field increased the safening effect to a level that may be commercially acceptable. The safening effect was only to cucumber as effective weed control was achieved with chloramben and naptalam.