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- Author or Editor: J.A. Menge x
Broadcasting, banding, and drilling were more effective in the field inoculation of plants with the vesicular arbuscular mycorrhizal fungus, Glomus deserticola Trappe, Bloss and Menge than seed inoculation or the application of lyophilized roots to both direct-seeded and transplanted citrus seedlings. Mechanized field inoculation of direct seeded and transplanted citrus seedlings is feasible, using fertilizer banding equipment, and seeding machines. In oculum remained consistently infective after soil inoculation for up to 2.5 months in fumigated field soil and for up to 1.5 months in mycorrhizal pot cultures of citrus grown in the greenhouse.
Tomato seedlings (Lycopersicon esculentum Mill. ‘Heinz 1350’) were inoculated with the vesicular-arbuscular mycorrhizal fungus Glomus fasciculatus (Thaxter) Gerd. & Trappe and either exposed to 30 pphm (589 μg/m3) ozone or to filtered air for 3 hours once weekly, beginning 3 weeks after inoculation, under long photoperiods (12–13.5 hr). Root infection by G. fasciculatus in ozone-exposed plants was retarded from week 3 to 5 compared to controls but recovered by week 7. Growth rates of mycorrhizal control plants were significantly greater than ozone-exposed mycorrhizal plants, but there were no differences in growth rates of nonmycorrhizal controls, mycorrhizal ozone-exposed plants, and nonmycorrhizal ozone-exposed plants. Under short photoperiods (less than 12 hr), growth rates of mycorrhizal controls were less than nonmycorrhizal controls and ozone did not significantly affect growth rates of nonmycorrhizal plants relative to controls. Leaf chlorophyll levels were similar whether plants were mycorrhizal, nonmycorrhizal, or exposed to ozone.
‘Troyer’ citrange [Poncirus trifoliata (L.) Raf. × Citrus sinensis (L.) Osbeck] seedlings were exposed to 82 ppm HCl for 20 minutes or 100 pphm ozone for 4 hours at 5, 12, and 16 weeks after inoculation with the vesicular-arbuscular mycorrhizal fungus, Glomus fasciculatus (Thaxter) Gerd. & Trappe. One group of citrange seedlings was exposed in a 2nd experiment to ozone at 90 pphm for 6 hours, once weekly, and a second group was exposed to 45 pphm for 3 hours, twice weekly for a period of 19 weeks beginning 1 week after fungal inoculation. Intermittent HCl and ozone exposures significantly reduced height and dry weight of mycorrhizal, but not of non-mycorrhizal plants. Fungal chlamydospore production was reduced 57% in ozone treatments but was not reduced by HCl exposures. Weekly exposures to 90 pphm ozone levels significantly reduced total dry weight in mycorrhizal plants by 42%, but reduced that of non-mycorrhizal plants by only 19%. However, 45 pphm ozone levels did not cause a similar reduction in either mycorrhizal or non-mycorrhizal plants. Mycorrhizal infection was reduced 15% and spore production 39% at 90 pphm ozone. The lower ozone level (45 pphm) reduced infection 22%, but had no effect on spore production. Absorption of phosphorus was not reduced by ozone treatments in either mycorrhizal or non-mycorrhizal plants.
Seedlings of ‘Topa Topa’ avocado (Persea americana Mill.) were grown in steamed loamy sand soil with no fertilizer, complete fertilizer (N, P, K, S, Ca, Mg, Cu, Zn, Mn, Fe, Mo, B), −P, −Zn, −P and −Zn, and −Zn+10 × P(640 ppm P). Seedlings were inoculated separately with one of 2 isolates of Glomus fasciculatus (Thaxter) Gerd. & Trappe (GF) or were inoculated with a water filtrate of the mycorrhizal inoculum plus autoclaved mycorrhizal inoculum. Growth of mycorrhizal seedlings was 49-254% larger than nonmycorrhizal avocados except at the −Zn+10×P regime where mycorrhizal and nonmycorrhizal avocados were of similar size. Both mycorrhizal isolates increased absorption of N, P, and Cu at all fertilizer treatments and absorption of Zn was increased with all fertilizer treatments by one mycorrhizal isolate. Fertilization with P did not alter P concentrations in leaves of nonmycorrhizal plants but increased P concentrations in leaves of mycorrhizal seedlings. Fertilization with 10×P increased P concentrations in both mycorrhizal and nonmycorrhizal seedlings. One GF isolate appeared to be superior to the other based on mineral nutrition of the host avocados. Differences between the isolates apparently were related to their rate of growth or ability to infect. Poor growth of avocado seedlings in steamed or fumigated soil can be related to poor mineral nutrition due to the destruction of mycorrhizal fungi.
Vesicular–arbuscular mycorrhizal inoculum consisting of a mixture of roots of coast redwood [Sequoia sempervirens (D. Don)], soil, and spores of Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappe was tested for viability and efficacy following storage for 4 or 8 weeks at 4, 9, 15, or 24C and moisture contents of 0%, 6%, 12%, or 17%. Storage regimes did not have any effect on the number of spores of Glomus mosseae recovered after storage. However, germinability of the spores decreased from 35% before storage to 10% to 31% during storage, especially under typical ambient room conditions (17% moisture at 24C). Maximum colonization of coast redwood, sierra redwood [Sequoiadendrom giganteum (Lindl.) Buchh.], and incense cedar (Libocedrous decurrens Torr.) was achieved after inoculation with 1 inoculum: 1 potting mix dilution (w/w). However, plant fresh weight was highest following inoculation with a 1 inoculum: 5 potting mix dilution (w/w). Dried inoculum was effective when stored at 24C, or below 10C when moist.
The length of time required for vesicular-arbuscular mycorrhiza (VAM) colonization, the effect of root age, and the position of VAM inoculum with respect to the root system were tested on cotton (Gossypium hirsutum L.), onion (Allium cepa L.), and pepper (Capsicum annuum L.). Colonization of onion by Glomus deserticola began 3 days after inoculation and reached 50% of the total root length after 21 days. Colonization by G. mosseae and G. intraradices began after 12 days and attained 15% and 37%, respectively, after 21 days. In cotton, colonization with G. deserticola and G. intraradices began 12 days following inoculation and increased to 20% and 18%, respectively, after 21 days. Colonization of cotton by G. mosseae was poor. In pepper, colonization with G. deserticola, G. mosseae, and G. intraradices began 3, 6, and 6 days after inoculation and, after 21 days, reached 60%, 13%, and 10%, respectively. In a second experiment, rapid colonization by G. deserticola took place in 3-day-old onion seedlings and increased to 51% 3 days after inoculation. Ten- and 17-day-old seedlings were far less responsive to VAM colonization but became highly infected at 30 days when new roots were produced. In a third experiment, inoculum placement 3 cm below seeds at planting in the field was the most effective for promoting colonization of cotton and onion by VAM. In fumigated field soil, mycorrhizae increased cotton growth an average of 28% when inoculum was applied below seeds compared to one- or two-sided band applications. Even in nonfumigated field soil, inoculum placed 3 cm below the seed and inoculum placed in a band at one side 2 weeks after planting significantly increased cotton growth. In onion, mycorrhizal inoculation improved growth in fumigated soil when it was placed below the seed, but did not stimulate growth in nonfumigated soil.
The effect of various integrated crop management practices on productivity (fruit yield, grade, and sire) and returns of `Washington Navel' oranges [Citrus sinensis (L.) Osbeck] was determined in the San Joaquin Valley of California. Seventy-two combinations of treatments comprised of three irrigation levels [80%, 100%, and 120% evapotranspiration demand (ETc)], three N fertilizer levels (low, medium, and high based on 2.3%, 2.5%, and 2.7% leaf N, respectively), gibberellic acid (±), miticide (±), and fungicide-nematicide (±) were included in the analysis. Using a partial budgeting procedure, returns after costs were calculated for each treatment combiition. Costs of treatments, harvesting, packing, and processing were subtracted from the value of the crop. The value of the crop was calculated as the sum of returns of crop in each size and grade category. The overall result indicated that returns after costs were higher for the +fungicide-nematicide treatment and also were generally more with increased irrigation. The combination of 120% ETc, +fungicide-nematicide, medium or high N, -miticide, and -gibberellin showed the highest return of all treatment combinations. Second highest returns were obtained with high N or with miticide and gibberellin used together.