Corn earworm (Helicoverpa zea) is a destructive pest with limited management options in sweet corn (Zea mays) production. Increased husk extension and the presence of the C-glycosyl flavone maysin are two proposed mechanisms for improving corn earworm resistance in corn cultivars. A factorial mating design was conducted to test hybrid combinations of sweet corn inbreds with long husks and/or maysin to identify candidates for future cultivar development. The mating design had seven male parents, including three commercial sweet corn inbreds (Wh9261, We11401, and Wt1001) and four inbreds selected for maysin content (Maysin1, 2, 3, and 4), and five female parents, including two commercial sweet corn inbreds (Ia453su and Ia5125su) and three inbreds with long, thick, tight husks (A684su, A685su, and A686su). Hybrids were evaluated for ear length, husk length, maysin content, and corn earworm resistance at six environments in 2016 and 2017. Relationships between husk extension, maysin, and corn earworm resistance were inconsistent, but five inbreds produced hybrids with significantly lower corn earworm infestation and/or damage, demonstrating potential to confer resistance to the corn earworm.
Virginia M. Moore and William F. Tracy
Weiting Huang and Zhongming Fang
The proliferation and differentiation of rhizomes are crucial for the propagation of Cymbidium species. We systematically assessed the effects of different concentrations of 20 amino acids on the proliferation and differentiation of C. goeringii rhizomes. Rhizome proliferation rates were significantly higher in media with 2.0 mmol·L−1 cysteine, 0.5 mmol·L−1 arginine, 0.2 mmol·L−1 asparagine, 1.0 mmol·L−1 proline, and 0.5 mmol·L−1 lysine compared with those in the control. Additionally, 1.0 mmol·L−1 tyrosine, 0.5 mmol·L−1 asparagine, and 0.2 mmol·L−1 aspartate were beneficial for rhizome differentiation. Furthermore, two combinations of amino acids, 0.5 mmol·L−1 arginine + 1.0 mmol·L−1 proline and 0.5 mmol·L−1 arginine + 2.0 mmol·L−1 cysteine, resulted in proliferation rates of 3.05 and 3.01, respectively, after 60 days. The highest differentiation rate (5.39 after 60 days) was observed in media with 0.5 mmol·L−1 asparagine + 0.2 mmol·L−1 aspartate. This study demonstrated that certain combinations of amino acids can effectively promote the proliferation and differentiation of rhizomes during the rapid propagation of C. goeringii.
Guirong Li, Ran Quan, Chaohui Yan, Xiaojin Hou, and Huiling Hu
Grape (Vitis vinifera) is among the world’s most important fruit crops and is a commonly used woody plant for genomics and post-genomics research. NAC transcription factors play central roles in plant growth and development, floral organ morphogenesis, and responses to biological stress. It is therefore important to identify key transcription factors from grape and clarify their mechanisms of action to generate genetic resources for grape molecular improvement. Our research group previously cloned a NAC transcription factor from V. vinifera ‘Yatomi Rosa’ [drought and leaf roll gene 1 (DRL1)] and demonstrated that it caused dwarfing of tobacco (Nicotiana benthamiana) plants when overexpressed. In the present work, we demonstrate that overexpression of DRL1 in transgenic tobacco delays flowering time and markedly reduces pollen viability. Furthermore, crosses between male DRL1 transgenic tobacco and female wild-type tobacco exhibit substantially lower fruit set, fruit and seed weights, fruit and seed shape indices, and seed germination rates than selfed wild-type plants or crosses with a transgenic female parent. DLR1 overexpression strongly influences flowering time and reproduction in transgenic tobacco, primarily through its effects on pollen development. These results provide a foundation for further functional characterization of DLR1 in grape.
Sylvia Cherono, Charmaine Ntini, Misganaw Wassie, Mohammad Dulal Mollah, Mohammad A. Belal, Collins Ogutu, and Yuepeng Han
The protective role of melatonin in plants under abiotic stress has been reported, but little information is available on its mitigation effect on coffee (Coffea arabica) plants. The objective of this study was to determine the effect of exogenous application of 100 µM melatonin in coffee leaves under 3 months of drought stress treatment. Melatonin was found to alleviate the drought-induced damage in coffee through reducing the rate of chlorophyll degradation, electrolyte leakage, malonaldehyde content, and activating various antioxidant enzymes, such as catalase, guaiacol peroxidase, and superoxide dismutase. Melatonin application suppressed the expression of chlorophyll degradation gene PAO encoding pheophorbide a oxygenase, and upregulated the expression of photosynthetic gene RBCS2 encoding ribulose-1,5-bisphosphate oxygenase (Rubisco) protein, and a drought-related gene AREB encoding abscisic acid-responsive element binding protein. The photosynthetic efficiency of photosystem II under dark adaptation was also improved upon melatonin application in drought-stressed plants. Our results showed that both foliar spray and direct soil application of melatonin could improve drought tolerance by regulating photosynthetic efficiency and oxidative damage in C. arabica seedlings. This study provides insights in application of melatonin as a protective agent against drought stress in improvement of crop yields.
Michael Stein, Corina Serban, and Per McCord
Seeds of sweet cherry (Prunus avium) possess a strong endodormancy response that traditionally requires months of stratification before germination can occur. Accelerating artificial dormancy release could be an important aspect of improving progress in a sweet cherry breeding program by increasing the first season growth period. In this study, seeds were exogenously treated with ethephon, 1-aminocyclopropane-1-carboxylic acid (ACC), kinetin, hydrogen peroxide, and acidified nitrite to attempt to induce germination with reduced stratification times. Findings showed that ethephon, ACC, and hydrogen peroxide all significantly increase early seed germination rates. Stratification time had the largest effect on increasing germinations, with significantly higher germination percentages accompanying increased stratification times that plateaued at 3 months of stratification. Stratification is vital for proper seedling development because plants grown from seeds with no stratification are significantly shorter and have reduced internode lengths compared with seeds with 4 weeks of stratification.
Gustavo F. Kreutz, Germán V. Sandoya, Gary K. England, and Wendy Mussoline
Lettuce (Lactuca sativa L.) is planted in Florida starting late fall at the end of September and continuing through the last harvest in May. In recent years, the season has shortened because of warm temperatures and weather-related events, such as rainfall at the beginning and the end of the season. During the transition between summer production in the Western U.S. lettuce season and the beginning of Florida’s winter production, there may be shortages of lettuce and other leafy vegetables in U.S. East Coast markets. In this research, we evaluated a set of lettuce breeding lines and cultivars in both sand and muck soils and a subset of romaine lettuces to determine whether lettuce planted in Florida’s sandy soils could help meet the supply shortage in the delay between the Western and Eastern U.S. lettuce seasons. Significant genetic variation and genotype × environment (G×E) interactions were observed among lettuce genotypes when planted in both sand and muck soils, suggesting that lettuce cultivars should be adapted and bred specifically for sandy soils. Romaine and butterhead lettuce lines produced higher yield in sandy soils; a particular romaine breeding line (BG18-0588) had good yield and less heat-related disorders when planted in warmer temperatures. Producing lettuce in sandy soils may have a higher production cost because of additional specific practices such as transplant production, plastic mulch, and fertigation, but these costs may be offset by increased productivity due to better weed control and nutrient timing. However, a future analysis should be conducted to elucidate the economic feasibility of producing lettuce in sandy soils.
Paul Kusuma and Bruce Bugbee
Phytochrome, a well-studied photoreceptor in plants, primarily absorbs in the red (R) and far-red (FR) regions and is responsible for the perception of shade and subsequent morphological responses. Experiments performed in controlled environments have widely used the R:FR ratio to simulate the natural environment and used phytochrome photoequilibrium (PPE) to simulate the activity of phytochrome. We review why PPE may be an unreliable metric, including differences in weighting factors, multiple phytochromes, nonphotochemical reversions, intermediates, variations in the total pool of phytochrome, and screening by other pigments. We suggest that environmental signals based on R and FR photon fluxes are a better predictor of plant shape than the more complex PPE model. However, the R:FR ratio is nonintuitive and can approach infinity under electric lights, which makes it difficult to extrapolate from studies in controlled environments to the field. Here we describe an improved metric: the FR fraction (FR/R+FR) with a range from 0 to 1. This is a more intuitive metric both under electric lights and in the field compared with other ratios because it is positively correlated with phytochrome-mediated morphological responses. We demonstrate the reliability of this new metric by reanalyzing previously published data.
Rita de Cássia Félix Alvarez, Aline Cordeiro Taveira, Sebastião Ferreira de Lima, Larissa Pereira Ribeiro Teodoro, Job Teixeira de Oliveira, Adriano dos Santos, Erina Vitório Rodrigues, Gessi Ceccon, and Paulo Eduardo Teodoro
This study aimed to identify promising crosses to generate cowpea breeding populations for the Brazilian Cerrado region. The experiment was carried out during the two crop seasons. The experimental design used was a randomized block with four replications and 20 genotypes prostrate. The effect of genotypes was significant for all traits evaluated. The Mahalanobis distance and the Tocher’s cluster were used to estimate the genetic diversity. Singh’s criterion was used to quantify the contribution of each trait to genetic diversity. Mass of hundred grains and grain yield were the traits that most contributed to detect diversity among cowpea genotypes. The crosses between the G14 genotype with G2, G3, G4, G5, G6, G11, G16, and G20 are promising for the development of populations with variability and high genetic potential.
Eric T. Wolske, Bruce E. Branham, and Kevin J. Wolz
The shade tolerance of black currants (Ribes nigrum cv. Consort) was studied by measuring the growth and productivity of mature plants in the field for three seasons under full sun or artificial shade netting in Urbana, IL. Shade treatments reduced photosynthetically active radiation (PAR) from 37% to 83%. Yield was not reduced in shade levels up to 65% but decreased by as much as 66% under 83% shade. Shade had minimal effect on stem rejuvenation in the first 2 years, but reduced rejuvenation in the third year from 14 new stems in full sun to eight new stems in 83% shade. Stem diameter decreased 8% to 19% with 83% shade, whereas no changes were observed in up to 65% shade. Plant height increased 5% to 8% from open sun to 83% shade. Specific leaf weight decreased and leaf area increased with shade. Powdery mildew severity increased with shade, and disease-resistant cultivars should be considered for understory crops. Our results indicate that growth and productivity of black currants can be maintained in moderate shade but shade levels beyond 65% will significantly reduce agronomic performance.
Ivette Guzman, Krystal Vargas, Francisco Chacon, Calen McKenzie, and Paul W. Bosland
This study investigated the diversity of carotenoids and phenolics in germplasm from three Capsicum (chile pepper) species, Capsicum annuum, Capsicum baccatum, and Capsicum chinense. Lutein, a yellow-pigmented carotenoid, and phenolics, a group of secondary metabolites, are reported to have health-promoting properties. The germplasm studied matured to a yellow color. The hypothesis was that all yellow fruits would contain either the carotenoid lutein, a yellow pigment, or a large amount of phenolics, a group of secondary metabolites that may be yellow among other colors. Thirty-one Capsicum accessions were grown in the field over a period of two seasons. On a dry weight (DW) basis, lutein ranged from 0.14 to 94.2 μg·g−1, and total phenolics ranged from 5.79 to 15.01 mg·g−1. No lutein was detected in one accession and β-carotene, another health-promoting compound, was lacking in four accessions. Accessions were grouped into four groups according to a principal component analysis plot. Results from this study indicate that in only nine accessions, lutein represented at least 50% of the total carotenoid amounts in each accession. These accessions are desirable not only as a source of dietary lutein, a natural yellow pigment, but also as genetic material that can be used to breed for higher lutein Capsicum. Therefore, yellow color is not a good indicator of lutein content and phytochemical analysis is required to determine the content of health-promoting compounds.