Optimization of Substrate and Nutrient Solution Strength for Lettuce and Chinese Cabbage Seedling Production in the Semi-Arid Environment of Central Myanmar

The growing population of tropical countries has led to a new awareness of the importance of vegetables as a source of essential foods and nutrients. The success of vegetable cultivation depends to a large extent on high-quality seedlings. This work aimed at evaluating the effects of different substrates and different nutrient solution concentrations on the development of lettuce and Chinese cabbage seedlings in a semi-arid tropical area. Three independent experiments were conducted at the Soil and Water Research Station at Yezin Agriculture University, Myanmar (Myanmar, 19.83° N; 96.27° E). In all experiments a randomized block design was implemented with four treatments and three repetitions. In the first experiment the adaptability of lettuce seedling to two substrates (namely a Hulls Manure mix composed by 50% of mature cattle manure and 50% of carbonized rice husk and a soil based substrate constituted by 70% local soil, 20% burned rice husk, and 10% fresh cattle manure) and two nutrient solutions with different electrical conductivities (ECs) (W0.1, stored rainwater with EC = 0.13 dS m−1 and NS1.2, nutrient solution with EC = 1.20 dS m−1) were tested. In the second and third experiments, two species (lettuce and Chinese cabbage) were assessed for their response to nutrient solution concentrations. In both crops, 4 fertigation treatments (W0.1; NS0.6; NS1.2; and NS1.8) were supplied, by modulating the concentration of a compound mineral fertilizer (15:15:15) in the following ranges: W0.1: 0 g L−1, electrical conductivity (EC) 0.13 dS m−1, NS0.6: 0.3 g L−1, EC of 0.60 dS m−1; NS1.2: 0.6 g L−1, 1.2 dS m−1 EC, and NS1.8: 0.9 g L−1, 1.8 dS m−1 EC. Adopting different substrates and applying different nutrient solutions significantly affected growth (fresh weight and leaf morphology) and some physiological parameters (stomatal conductance, leaf temperature, and leaf chlorophyll content) of lettuce and Chinese cabbage seedling. From the first experiment, the combination of the soil based substrate and NS1.2 treatments allowed us to improve the seedlings’ growth. In the second experiment, highest growth of lettuce and Chinese cabbage seedlings was associated with NS1.2 and NS1.8, respectively. The presented results allow for the optimization of both growing media and nutrient solution management when lettuce and Chinese cabbage seedling are produced in the Central Dry Zone of Myanmar.

Herbicidal potential of Araucaria angustifolia (Bertoloni) Otto Kuntze in lettuce seedlings in vitro

Araucaria angustifolia (Bertoloni) Otto Kuntze plants are a viable source of potentially active secondary metabolites; however, deep studies and researches about the activity of these compounds are needed. The objective of this work was to assess the herbicidal activity of ethanolic extracts of plants of the species A. angustifolia in lettuce seedlings in vitro. Ethanolic extracts at different concentrations (0,0%, 12.5%, 25.0%, 50.0%, and 100.0%) were prepared using barks and leaves. A semisolid MS medium with pH adjusted to approximately 5.7 was prepared, solidified with 8g L-1 of agar, and autoclaved at 1.6atm for 20 minutes. The extracts were added to the culture medium during their preparation before the autoclaving, using an automatic pipette containing 0.1mL of A. angustifolia extract per lettuce seedling. The number of leaves per seedling, seedling height, chlorophyll content, root and shoot dry weights, and mortality percentage was determined at 20 days after inoculation. The results showed that the extract from leaves or barks of A. angustifolia plants has herbicidal activity in lettuce seedlings in vitro, and the extract concentration of 100% presented the best inhibitory results for the variables evaluated.

Large Scale Screening of Rhizospheric Allelopathic Bacteria and Their Potential for the Biocontrol of Wheat-Associated Weeds

Conventional weed control practices have generated serious issues related to the environment and human health. Therefore, there is a demand for the development of alternative techniques for sustainable agriculture. The present study performed a large-scale screening of allelopathic bacteria from the rhizosphere of weeds and wheat to obtain biological weed control inoculants in the cultivation of wheat. Initially, around 400 strains of rhizobacteria were isolated from the rhizosphere of weeds as well as wheat that grows in areas of chronic weed invasions. A series of the screen was performed on these strains, including the release of phytotoxic metabolites, growth inhibition of sensitive Escherichia coli, growth inhibition of indicator plant of lettuce, agar bioassays on five weeds, and agar bioassay on wheat. Firstly, 22.6% (89 strains) of the total strains were cyanogenic, and among the cyanogenic strains, 21.3% (19 strains) were inhibitory to the growth of sensitive E. coli. Then, these 19 strains were tested using lettuce seedling bioassay to show that eight strains suppressed, nine strains promoted, and two strains remained ineffective on the growth. These 19 strains were further applied to weeds and wheat on agar bioassays. The results indicated that dry matter of broad-leaved dock, wild oat, little seed canary grass, and common lambs’ quarter were reduced by eight strains (23.1–68.1%), seven strains (38.5–80.2%), eight strains (16.5–69.4%), and three strains (27.5–50.0%), respectively. Five strains suppressed the growth of wheat, nine strains increased its dry matter (12.8–47.9%), and five remained ineffective. Altogether, the strains that selectively inhibit weeds, while retaining normal growth of wheat, can offer good opportunities for the development of biological weed control in the cultivation of wheat.

Preliminary screening of rhizobacteria for biocontrol of little seed canary grass (Phalaris minor Retz.) and wild oat (Avena fatua L.) in wheat

Conventional weed control methods often have environmental impact. The present study was conducted to screen selected accessions of Pseudomonas for both potential biocontrol of Phalaris minor and Avena fatua and potential concurrent growth promotion of wheat. The four Pseudomonas strains (B11, T19, T24, and T75) were found positive for cyanide production, siderophore production, phosphorus solubilization, oxidase activity, catalase activity, and ACC deaminase activity in vitro. These strains were phytotoxic, causing up to 73.3% mortality in the lettuce seedling bioassay. Consortia of compatible Pseudomonas strains increased A. fatua and P. minor seedling mortality up to 50.0% and 56.7%, respectively, and reduced root length up to 73.8% and 53.9%, respectively, as compared with the uninoculated control. Consortia of compatible Pseudomonas strains increased wheat shoot length, root length, fresh biomass, dry biomass, and leaf greenness up to 41.6%, 100%, 79.9%, 81.5%, and 21.1%, respectively, over the uninoculated control. Four of the 11 Pseudomonas consortia tested expressed good weed suppression and wheat growth promotion capacity and deserve further experimentation. The findings from this study may lead to the formulation of bioherbicides that will improve human and environmental health.

Efficiency of biocompost potentiated with chemical fertilizer and facilitated aeration

The aims were to reduce composting time, to evaluate the application of produced composts and to size two composting yards (conventional and potentiated). Eight compost heaps with 400 kg of food industry or urban organic waste were built: 1) control; 2) facilitated aeration; 3) potentiated with facilitated aeration and chemical fertilizer; and 4) chemical fertilizer. The analyzed parameters were pH, temperature, humidity and C/N ratio. Compost heap reached stabilization at 90 days without chemical fertilizer and at 25 days when potentiated, regardless of the waste origin. Stabilized composts were applied to lettuce crop under natural conditions and compared with commercial compost. Composts with chemical fertilizer were the most effective in enabling lettuce seedling growth. For medium-sized cities, the conventional composting yard requires 6.58 ha, whereas the potentiated composting yard requires 1.69 ha, considering the recorded stabilization time of 90 and 25 days, respectively. The potentiated composting was the most efficient because its shorter stabilization time, did not require manual turning and produced compost with higher nutrient content. Besides that, requires an area 74.32% smaller than the conventional yard, fact that enables using this process to treat industrial and urban solid organic waste.

Potential of aqueous extracts of basidiomycetes to control root-knot nematodes on lettuce

ABSTRACT The root-knot nematode (Meloidogyne incognita) is one of the main pests of lettuce due to the crop’s high susceptibility, unavailability of registered nematicides and lack of resistant cultivars. The aim of this study was to evaluate the potential of aqueous extracts of ten basidiomycete fungi for root-knot nematode control (in vitro and in vivo) on lettuce. The aqueous extracts of these fungi were initially evaluated in vitro in relation to their nematostatic and nematicidal activity. All extracts inhibited the hatching of second-stage juveniles of nematodes. The extracts that provided the highest mortality index (Pleurotus ostreatus, P. citrinopileatus, P. pulmonarius and Boletus sp.) were applied in pots containing autoclaved and infested soil with root-knot nematode. After 24 h, one lettuce seedling (cv. Regina) per pot was transplanted using soil treated with distilled water as control. After 50 days, we observed that soil treated with fungal extracts reduced, approximately, 70% of nematode reproduction. Plants treated with extracts obtained higher fresh mass and extracts of Boletus sp. and P. pulmonarius reduced damages to roots, being considered as potential bio-controllers of this nematode.