Effect of plant bio-regulators on photosynthesis, growth and yield efficiency of pear trained on Y-trellis system

‘Patharnakh’ and ‘Punjab Beauty’ are major pear cultivars grown under the subtropical conditions of northwestern India. These pear cultivars tend to put up profuse vegetative growth under the high density planting that leads to excessive shading of bearing zone of canopy. To facilitate light penetration into inner plant canopy, there is a need to contrive an efficient approach for vegetative growth management. The foliar applications of varying concentrations of plant bio-regulators viz. Prohexadione calcium (Pro-Ca) (100, 200, 400 mg L-1) and Paclobutrazol (PBZ) (100, 250, 500 mg L-1) were done at 10 days after full bloom (DAFB) ‘Patharnakh’ and ‘Punjab Beauty’ pear plants trained on the Y-trellis training system. Shoot length, leaf area index and trunk cross-sectional areas (TCSA) were greatly reduced by Pro-Ca200 and 400 mg L-1 concentrations. Treatments enhanced light penetration and photosynthesis. Fruit weight improved with plant bio-regulator treatments resulting in increased yield efficiency of pear plants. This study exhibited a strong positive correlation between light availability and yield efficiency of pear plants.

Are prohexadione calcium and Pseudomonas fluorescens a solution to limit the spread of annual bluegrass (Poa annua L.) on football pitches?

In 2020, a greenhouse experiment was conducted to investigate the suppression of annual bluegrass (Poa annua), which is a difficult weed to manage in cool-season in turfgrass mixtures on football pitches. The efficacy of prohexadione calcium (Pc), ethephon (Eth) and Pseudomonas fluorescens against P. annua, Lolium perenne and Poa pratensis was tested, as the latter two most commonly occur in turfgrass mixtures on football pitches. Mesotrione (Mes) was used as a positive control, and nontreated grass was used as a negative control. Only a single grass species was sown in each pot. Treatments were randomly distributed for two experiments conducted separately: first – unmown grass before the beginning of spraying and second – grass mowed before the beginning of spraying. In both experiments, plant height and the number of tillers were measured/counted several times during the growing season. In both experiments, grasses were sprayed six times with Pc, Eth and P. fluorescens, while Mes was applied twice. Based on the performed study, the efficacy of the tested products is connected to grass species and whether the grass was mowed/cut before spraying. It has been detected in the present study that spraying with Pc could reduce the height of annual bluegrass, while spraying with P. fluorescens has reduced the number of tillers. Spraying was more effective on grasses that were mowed/cut before the beginning of spraying. Mes should cause severe damage to annual bluegrass but without confirmation in this study. Results of this study have indicated that the application of Pc and P. fluorescens can inhibit the spread of annual bluegrass in football pitches; however, testing their effectiveness against P. annua under field conditions should be performed as well.

Effects of Prohexadione Calcium Applications on Growth and Yield Characteristics of Cucumber (Cucumis sativus L.)

This study was conducted to determine the effects of growth regulator prohexadione calcium (Pro-Ca) and inhibitor gibberellic acid on some parameters (yield, pigment levels of leaves, nutrient contents, proline, enzyme activities and fruit quality) when applied at different doses (0, 15, 30, 45, and 60 mg L-1). Chemicals were applied after transplanting seedlings. A total of 12 plots including 3 plants for each dose were used in randomised plot experimental design. Although it has a positive effect on leaf proline content and enzyme activities, 45, and 60 mg L-1 doses of Pro-Ca had negative effects on morphological parameters (excluding stem diameter), yield, leaf pigment (excluding chlorophyll a) and nutrient contents compared to control. High Pro-Ca doses generally affected the fruit quality properties positively while 15 mg L-1 of Pro-Ca did not affect other parameters, except decreasing fruit yield. A 30 mg L-1 of Pro-Ca dose was the most positive effective dose on the examined parameters. The highest vegetative development, yield, nutrient uptake and proline content were obtained from the plants subjected to 30 mg L-1 of Pro-Ca dose. Moreover, this dose increased fruit firmness, TSS, EC values and enzyme activities compared to control. Being an important quality criterion in cucumber storage after harvest, the weight loss rate 29.4% was lower in fruits obtained from the plant having 30 mg L-1 of Pro-Ca dose compared to that of the control plants. Therefore, 30 mg L-1 of Pro-Ca application, beside its positive effects on plant growth, yield and fruit quality, can be suggested for also increase shelf life of fruits in cucumber cultivation in greenhouse.

Gibberellins Inhibit Flavonoid Biosynthesis and Promote Nitrogen Metabolism in Medicago truncatula

Bioactive gibberellic acids (GAs) are diterpenoid plant hormones that are biosynthesized through complex pathways and control various aspects of growth and development. Although GA biosynthesis has been intensively studied, the downstream metabolic pathways regulated by GAs have remained largely unexplored. We investigated Tnt1 retrotransposon insertion mutant lines of Medicago truncatula with a dwarf phenotype by forward and reverse genetics screening and phylogenetic, molecular, biochemical, proteomic and metabolomic analyses. Three Tnt1 retrotransposon insertion mutant lines of the gibberellin 3-beta-dioxygenase 1 gene (GA3ox1) with a dwarf phenotype were identified, in which the synthesis of GAs (GA3 and GA4) was inhibited. Phenotypic analysis revealed that plant height, root and petiole length of ga3ox1 mutants were shorter than those of the wild type (Medicago truncatula ecotype R108). Leaf size was also much smaller in ga3ox1 mutants than that in wild-type R108, which is probably due to cell-size diminution instead of a decrease in cell number. Proteomic and metabolomic analyses of ga3ox1/R108 leaves revealed that in the ga3ox1 mutant, flavonoid isoflavonoid biosynthesis was significantly up-regulated, while nitrogen metabolism was down-regulated. Additionally, we further demonstrated that flavonoid and isoflavonoid biosynthesis was induced by prohexadione calcium, an inhibitor of GA3ox enzyme, and inhibited by exogenous GA3. In contrast, nitrogen metabolism was promoted by exogenous GA3 but inhibited by prohexadione calcium. The results of this study further demonstrated that GAs play critical roles in positively regulating nitrogen metabolism and transport and negatively regulating flavonoid biosynthesis through GA-mediated signaling pathways in leaves.

Alfalfa Established Successfully in Intercropping with Corn in the Midwest US

Integrating alfalfa (Medicago sativa L.) with corn (Zea mays L.) for grain will increase biodiversity, reduce the negative environmental impact of corn monoculture and increase farm profitability. The objectives of this research were to evaluate forage productivity and nutritive value, along with stand establishment of alfalfa in a corn grain system in Iowa, Minnesota, and North Dakota. The experimental design was a randomized complete block with four replicates at each site. Treatments included were: sole corn (i.e., check; T1), sole alfalfa (T2), alfalfa intercropped into corn (T3), a prohexadione-treated alfalfa intercropped with corn (T4), and a spring-seeded alfalfa in the year after intercropping (T5), which was planted in plots with T1 the previous year. All sites had below normal rainfall in 2016 and 2017. Corn grain yield was significantly lower when intercropped with alfalfa (T3 and T4) compared with the check corn crop (no alfalfa, T1). Corn grain yield reduction ranged from 14.0% to 18.8% compared with the check (T1). Corn biomass yield was reduced by intercropped alfalfa (T3 and T4) by 15.9% to 25.8%. In the seeding year, alfalfa seasonal forage yield was significantly greater when corn competition was absent in all environments. The intercropped alfalfa from the previous season (T3 and T4) had almost double the forage yield than the alfalfa in the seeding year (spring-seeded alfalfa; T5). In the second production year, there were no meaningful forage yield differences (p > 0.05) across all treatments, indicating alfalfa in intercropping systems does not affect forage yield past the first production year. Prohexadione-calcium, a growth regulator, did not affect alfalfa stand density, forage yield and nutritive value. The forage nutritive value was dependent on harvest date not the alfalfa intercropping treatments. Results of our study suggest that establishing alfalfa with corn is feasible and can be a potential alternative for the upper Midwest region. However, when under drought conditions, this system might be less resilient since competition between alfalfa and corn for soil moisture will be intensified under drought or moisture-limited conditions, and this will likely depress corn grain yield. Research targeted to reintroduce perennial crops into the current dominant corn–soybean systems in the US Corn Belt is urgently needed to improve stability and resiliency of production systems.