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G.S. Guzman, I.C.A Alvarez, and L.J. Farias

In the commercial production of silver king plants and other ornate plants, the substrates are treated with fungicides, which affect the vesicular–arbuscular mycorrhizal (VAM) fungi and the plant growth negatively. The restoration of de VAM fungi to the substrate, after its disinfection, might improvement the development. The effectiveness and infectiveness of Glomus fasciculatum and Glomus aggregatum on silver king (Aglaonema commutatum) plants was evaluated in this work. Seedlings of 4-week-old, growing treated with mancozeb, were removed and planted in pots filled with a disinfected mixture of sand soil, cow manure and coconut powder (1:2:2), containing the inoculum of VAM fungi (soil with spores and colonized roots). After 3 and 4 months of the inoculation, plants were removed and dry weight of roots and shoot, number and length of leaves, and mycorrhizal colonization were evaluated. A better development was showed in plants inoculated, resulting highest values in number and length of leaves in relation to control plants. Both VAM fungi improvement the number and length of leaves. The percentage root length colonized (80%) and visual density of endophyte in roots was highest in plants inoculated with Glomus aggregatum in both sampling period.

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J. Farías-Larios, J.G. López-Aguirre, J.L. Miranda, and L.A. Bayardo-Vizcaino

Acerola (Malpighia glabra L.) is a small, red fruit that is native to the West Indies, but is also grown in South and Central America. In western Mexico, this crop is very important because acerola is the richest known natural source of vitamin C, with a content of 1000 to 4500 mg/100 g of fruit. In nursery and field conditions, acerola growth is severely affected by root-knot nematode. The objective of this study was to evaluate the use of commercial formulations of Bacillus spp. on root-knot nematode management. This study was carried out in the Farm Santa Clara Maria in Colima State. Acerola plants, 60 days old were used. They were grown in 3-L pots with soil, compost, and pumice stone mixture as substrate. Treatments evaluated were: 5, 10, 15 and 30 mL/pot of Activate 2001, Tri-Mat (5 mL/pot) and control, without application. Activate 2001® is a concentrated liquid in water suspension of Bacillus chitinosporus, B. laterosporus, and B. licheniformis. Initial nematode population was of 3,305 in 50 g of roots. Acerola plants were harvested at 30, 60, and 90 days after application. Results show that Activate 2001 at 10 and 30 mL rates reduce significantly root-knot populations in acerola plants 60 days after application with 135 and 178 nematodes/50 g of roots, respectively. Diameter stem, shoot fresh and dry weight and root production were also increased by rhizobacteria application. These results are promising and confirmed the potential of Bacillus as a biological agent for nematode management.

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G.S. Guzmán, O.C.E. Cuevas, L.J. Farias, and S.M. Orozco

Citrus macrophylla is an important citrus rootstock for Mexican lemon (Citrus aurantifolia S.). Citrus are highly dependent of vesicular–arbuscular mycorrhizal (VAM) fungi. Four Glomus species were screened for their symbiotic response with C. macrophylla. Seedlings were inoculated with VAM fungi in pots containing sterilized soil. After 3 and 4 months, plants were harvested. Glomus fasciculatum (following by G. intraradices) gave the greatest improvements in growth, resulting in larger plant height and higher shoot dry weight. Glomus aggregatum, G. mosseae, and control plants showed the lowest rates of growth. Plants inoculated with the first three species showed the highest percent of root length colonized. However G. aggregatum gave the highest values of visual density of endophyte in root and soil hyphae. Root colonization and soil hyphae were lowest in plants with G. mosseae.

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Timothy L. Righetti, Carmo Vasconcelos, David R. Sandrock, Samuel Ortega-Farias, Yerko Moreno, and Francisco J. Meza

Net photosynthetic rates often are dependent on leaf size when expressed on a leaf-area basis (CO2 assimilation as μmol·m−2·s−1). Therefore, distinguishing between leaf-size-related and other causes of differences in net photosynthetic rate cannot be determined when data are presented on a leaf-area basis. From a theoretical perspective, CO2 assimilation expressed on a leaf-area basis (μmol·m−2·s−1) will be independent of leaf area only when total net CO2 assimilation (leaf CO2 assimilation as μmol·s−1) is linearly related to leaf area and the function describing this relationship has a nonzero y intercept. This situation was not encountered in the data sets we evaluated; therefore, ratio-based estimates of CO2 assimilation were often misleading. When CO2 assimilation data are expressed on a per-leaf-area basis (the standard procedure in the photosynthesis literature), it is difficult to determine how photosynthetic efficiency changes as leaves or plants mature and difficult to compare the efficiency of treatments or cultivars when leaf size or total plant leaf area varies.