The root-knot nematode (M. hapla Chitwood) poses a threat to carrot (Daucus carota L.) production in the United States. Little information is available concerning the genetic control of nematode resistance in carrot. Crosses between two inbreds, a resistant genotype (R1) and susceptible genotype (S1) identified in previous screening tests of carrot were studied in the F2 and BC1 generations to determine the heritability of resistance to the root-knot nematode. Seedlings of F2 (R1/S1), BC1S1, and BC1R1 generations were evaluated for their responses to infestation of M. hapla Chitwood based on gall number per root, gall rating per root, and root rating per root in a greenhouse experiment conducted during 1994. Narrow-sense heritabilities were calculated according to the method of Warner (1952). Narrow-sense heritability was 0.16 for resistance based on gall number, 0.88 for resistance based on gall rating, and 0.78 for resistance based on root rating. This information may be of importance to geneticists and carrot breeders for the development of nematode-resistant carrot cultivars.
Min Wang and Irwin L. Goldman
Genetic relationships among 37 accessions of Beta vulgaris, including 21 table beet, 14 sugar beet, and two Swiss chard (Beta vulgaris ssp. cicla) accessions, were evaluated using randomly amplified polymorphic DNA (RAPD). Genetic distance was estimated based on the presence or absence of polymorphic RAPD bands. Multidimensional scaling plots of genetic distance values revealed that table beet inbred lines from the University of Wisconsin Table beet Breeding Program clustered in an intermediate position between sugar beet breeding lines and standard table beet germplasm, likely because of their origin from an introgression program designed to incorporate sugar beet genes.
Min Wang and I.L. Goldman
The genetics of resistance to root-knot nematode (M. hapla Chitwood) was studied in crosses of three carrot inbred genotypes, two resistant genotypes (R1 and R2) and one susceptible genotype (S1) identified in previous screening tests. Seedlings of three parental genotypes, six F1 crosses including three reciprocal crosses, two BC1 populations, and three F2 populations were evaluated for their resistance and susceptibility to infestation of M. hapla Chitwood based on gall number per root, gall rating per root, and root rating per root in a greenhouse experiment carried out in 1994. All six F1 plants were susceptible, which indicated a lack of heterosis for resistance in these F1s. The R1 × S1 cross segregated 3 susceptible: 1 resistant in the F2, 1 susceptible: 1 resistant in the BC1R1, and did not segregate in the BC1S1. The R1 × R2 cross yielded 44 susceptible: 36 resistant seedlings in the F2 (R1R2), and 48 susceptible: 32 resistant in the reciprocal cross of R1 and R2, both of which closely fit a 9: 7 ratio (P ≤ 0.001). These results indicate these two resistant genotypes carry two different homozygous recessive genes conditioning root-knot nematode resistance. We propose a model of duplicate recessive epistasis control the reactions of host plants and nematode in these crosses.
Min Wang and I.L. Goldman
Governmental recommended allowances for folic acid have increased dramatically in recent years, especially for pregnant women. Red beet is an important vegetable source of folic acid; however, little is known about the extent of variation for native folic acid content in red beet genotypes. The objective of this investigation was to evaluate variation in folic acid content (FAC) among red beet hybrids (F1), inbred lines (IL), plant introductions (PI), and open-pollinated cultivars (OP). Eighteen genotypes, including 12 F1 and six OP, were evaluated in field experiments during both years. Averaged over years, highly significant differences among genotypes and between F1 and OP were detected. FAC ranged from 3.7 mg to 15.2 mg per gram dry weight. The FAC in OP was 13% higher than in F1. Thirty genotypes, including 13 IL and 17 PI, were evaluated in greenhouse experiments during 1993 and 1994. Highly significant differences among genotypes and between IL and PI were detected. FAC varied from 1.54 mg to 11.13 mg per gram dry weight. The FAC in IL was 43% higher than in PI. These results demonstrate an approximate 10-fold variation among red beet genotypes for FAC.
Min Wang and Mark W. Farnham
Downy mildew, caused by Peronospora parasitica (Pers. ex Fr.), is one of the most economically important diseases in broccoli (Brassica oleracea L. Italica group). Previous studies reported that resistance to downy mildew in broccoli depends on plant age and that seedling resistance appears to be independent of mature-plant resistance. The objectives of our studies were to evaluate resistance and susceptibility of USDA broccoli inbreds to downy mildew and to investigate the interaction between the host and pathogen at two plant stages with single or double inoculation. Multiple screening tests at both cotyledon and three-expanded leaf stages using 38 entries, including USDA inbreds and commercial hybrids, were conducted in randomized complete-block designs. In these tests, every leaf of each plant was thoroughly sprayed with P. parasitica isolate PP1 at a concentration of 10,000 sporangia per ml at both stages. Ratings for downy mildew reaction phenotype were made at 9 days postinoculation on a 0-9 scale of increasing disease severity. We found significant phenotypic variation to infection among broccoli entries. We observed three general phenotypes: 1) resistance at both stages; 2) susceptible at cotyledon stage combined with resistance at three-expanded leaf stage; and 3) susceptibility at both stages. Additionally, inoculation at the cotyledon stage had no effect on inoculation at the three-expanded leaf stage.
Xin Song, Suo-min Wang, and Yiwei Jiang
Perennial ryegrass (Lolium perenne) is a popular cool-season and forage grass around the world. Salinity stress may cause nutrient disorders that influence the growth and physiology of perennial ryegrass. The objective of this study was to identify the genotypic variations in growth traits and nutrient elements in relation to salinity tolerance in perennial ryegrass. Eight accessions of perennial ryegrass [PI265351 (Chile), PI418707 (Romania), PI303012 (UK), PI303033 (The Netherlands), PI545593 (Turkey), PI577264 (UK), PI610927 (Tunisia), and PI632590 (Morocco)] were subjected to 0 (control, no salinity) and 300 mm NaCl for 10 d in a greenhouse. Across accessions, salinity stress decreased plant height (HT), leaf fresh weight (LFW), leaf dry weight (LDW), leaf water concentration (LWC), and concentration of N, C, Ca2+, Cu2+, K+, Mg2+, and K+/Na+ ratio and increased Na+ concentration. Negative correlations were found between C and Na+, whereas positive correlations of K+/Na+ with C and N were found under salinity treatment. The principal component analysis (PCA) showed that the first, second, and third principal components explained 40.2%, 24.9%, and 13.4% variations of all traits, respectively. Based on loading values from PCA analysis, LWC, Na+ concentration, and K+/Na+ ratio were chosen to evaluate salinity tolerance of accessions, and eight accessions were divided into the tolerant, moderate, and sensitive groups. The tolerant group had relatively higher LWC and K+/Na+ ratio and concentrations of C, P, and Fe2+ and lower Na+ concentrations than the other two groups, especially the sensitive groups. The result suggested that lower Na+ accumulation and higher K+/Na+ ratio and LWC were crucial strategies for achieving salinity tolerance of perennial ryegrass.
Xue-Min Hou, Zi-Hua Wang, Xi-Min Deng, and Guo-Hui Li
This experiment was carried out to obtain a pressure–volume (P-V) curve and Höfler diagram of the cortex tissue of fresh ‘Fuji’ apple fruit (Malus ×domestica Borkh.) with a novel centrifuge method. Based on the P-V curve and Höfler diagram, several water relation parameters of cortex tissue were determined and the interrelationship of these parameters was established. Turgor loss point (TLP) occurred at –1.74 MPa and 73.7% of relative water content (R*). At full hydration, osmotic potential (ψS) was –1.30 MPa and symplastic water accounted for 86.8% of R*. Bulk elastic modulus decreased linearly by 28% as pressure potential declined from 1.30 MPa at full hydration to zero at the TLP. This centrifuge technique can provide a simple and efficient way to determine water relation parameters of fleshy fruits.
Shiow Wang, Kimberly Lewers, Linda Bowman, and Min Ding
Representatives of three species of strawberries (Fragaria virginiana, F. chiloensis and F. ×ananassa) were evaluated for antioxidant capacity, scavenging capacity for reactive oxygen species (ROO·, ·OH, 1O2 and O2 .-), and inhibitory effect on proliferation of A549 human lung epithelial cancer cells. Differences among the strawberry genotypes were observed for all three qualities. High antioxidant and scavenging capacities were found in `CFRA 0982', `JP 95-1-1', NC 95-19-1 and RH 30. Lowest antioxidant and scavenging capacities were found in `Allstar'. There was also a relationship between scavenging capacity and the inhibition of cancer cell proliferation. The correlations (R 2) between the scavenging capacities for the reactive oxygen species and the inhibition of cancer cell proliferation were 0.8074, 0.8279, 0.7862 and 0.7761 for ROO·, ·OH, 1O2 and O2 .-, respectively. These results suggest that antioxidants, specifically their scavenging capacities, may play an important role in the antiproliferative activity of strawberries. This study also identified strawberry germplasm of value in developing cultivars useful for cancer prevention.
Min Wang, Mark W. Farnham, and Claude E. Thomas
Downy mildew, caused by Peronospora parasitica (Pers. Fr.) Fr., is one of the most economically important diseases of broccoli (Brassica oleracea L. Italica group). Previous studies have shown that resistance to downy mildew in broccoli is dependent on plant age with seedling resistance being independent of mature-plant resistance. The objectives of this study were to: 1) determine if valid evaluations for downy mildew resistance can be conducted at both the cotyledon and the three to four true-leaf stages on the same plants of a given broccoli entry; 2) determine if doubled-haploid (DH) lines derived from the resistant hybrid `Everest' also exhibit resistance to downy mildew and if so, characterize the resistance phenotype(s) in these lines; and 3) determine if identified resistant DH lines exhibit resistance to isolates of P. parasitica acquired from different geographic regions of the United States. Twenty-three DH broccoli inbreds and two commercial hybrids were evaluated for reaction at different developmental stages to infection by P. parasitica in a controlled environment. Results showed that broccoli plants can be evaluated for downy mildew resistance in a two-stage process. Inoculation at the cotyledon stage did not offer any cross-protection or otherwise influence the expression of reaction phenotype (RP) when the same plants were subsequently inoculated at the three to four true-leaf stage. Three different RPs to infection by P. parasitica were identified in DH inbreds. These were: 1) susceptibility at both the cotyledon stage and the true-leaf stage; 2) resistance at both the cotyledon and true-leaf stage; and 3) susceptibility at the cotyledon stage but resistance at the true-leaf stage. There was no effect of two pathogenic isolates from different geographic regions on RP of DH broccoli inbreds. Selection of plant resistance to downy mildew at the cotyledon stage will effectively identify plants with high levels of resistance at subsequent developmental stages.
Min Wang, Mark W. Farnham, and Claude E. Thomas
Downy mildew, incited by the biotrophic fungal parasite, Peronospora parasitica (Pers. Fr.) Fr., is one of the most destructive diseases of broccoli (Brassica oleracea L., Italica Group) and other related crop species throughout the world. Cultivation of resistant cultivars is the most desirable control method because it provides a practical, long-term, and environmentally benign means of limiting damage from this disease. The commercial hybrid cultivar, Everest, has been shown previously to contain a high level of downy mildew resistance. Doubled-haploid (DH) lines developed from that hybrid were also shown to exhibit a similar, high level of resistance at the three- to four-leaf stage. To determine the mode of inheritance of this true leaf resistance, the resistant DH line was crossed to a susceptible line (derived from `Marathon') to produce an F1 hybrid. Subsequently, F2 and backcross (BC) populations were developed from the hybrid. In addition, a DH population of ≈100 lines was developed from the same F1 used to create the F2 and BC. All populations were evaluated for response to artificial inoculation with P. parasitica at the three- to four-leaf stage. F1 plants were resistant like the resistant parent and F2 populations segregated approximately nine resistant to seven susceptible. Using the resistant parent as recurrent parent, BC populations contained all resistant plants, while the BC to the susceptible parent fit a 1 resistant: 3 susceptible segregation ratio. These results can be explained by a model with two complementary dominant genes. This model was confirmed by the DH population that segregated ≈1:3, resistant to susceptible. Due to the dominant nature of this resistance, controlling genes should be easily incorporated into F1 hybrids and used commercially to prevent downy mildew.