Growth Reduction of Apple Seedlings by Pratylenchus penetrans as Influenced by Seedling Age at Inoculation.

Apple seedlings of different ages (1, 3, and 5 weeks) were inoculated with 6,900 Pratylenchus penetrans per seedling in 10-cm-diam pots in a growth chamber. Rate of growth suppression and total growth suppression of seedlings by P. penetrans were inversely proportional to seedling age at time of nematode inoculation. Younger seedlings were found to contain a higher number of nematodes per gram root.

Effect of Soil Water Potential on Growth of Apple Trees Infected with Pratylenchus penetrans.

Malling-Merton 106 apple rootstocks inoculated with Pratylenchus penetrans, or uninoculated, were grown in a growth chamber in pots of loamy sand maintained at two moisture levels, 0 to -0.4 bar or 0 to -10 bars. Either inoculation or low soil moisture suppressed shoot growth and increased root necrosis. However, the nematode-soil moisture interaction was not significant.

Growth response of three vegetables to smooth- and crenate-tailed females of three species of pratylenchus.

The effect of morphological variants of females of Pratylenchus penetrans, P. neglectus, and P. crenatus on the growth of three vegetables was studied. Variants were characterized by having either a smooth or crenate tail terminus. Pea was inoculated with variants of P. penetrans, one female per seedling, and grown at light intensities ranging from 1,350 to 21,600 lux in a series of five experiments. Only crenate-tailed females of P. penetrans suppressed the growth of pea and only when pea was grown at 3,900 lux. Radish was inoculated with morphological variants of P. penetrans, P. neglectus, and P. crenatus, four females per seedling, and grown at 3,900 lux in two experiments. Again, truly creuate-tailed females of P. penetrans inhibited growth. The two variants of P. penetrans had a similar infectivity, greater than that of the other two species of Pratylenchus. Only crenate-tailed P. penetrans reproduced on radish. Onion was inoculated with variants of P. penetrans and P. crenatus, four females per seedling, and grown at 14 C at 12,900 lux. Again, only crenate-tailed P. penetrans inhibited growth. The variants of P. penetrans had a similar infectivity, greater than that of P. crenatus. Neither species reproduced on onion at low temperatures.

Worldwide distribution of potato-cyst nematodes and their importance in crop production.

The potato-cyst nematodes Heterodera rostochiensis and H. pallida are important pathogens of potatoes, a basic food crop. When soil populations of either species are high, potato yields are often less than the seed planted. Apparently, these nematodes originated in the Andean mountains of South America, the home of the potato. One or both species have spread from this region to approximately 47 countries. The two species may occur together or separately in potato-growing areas. Although these nematodes can be spread in numerous ways, contaminated soil associated with seed potatoes, farm machinery, and reusable containers is among the most important. An integrated control program used in the U.S.A. is described.

Morphological variation in Pratylenchus penetrans.

Variability of morphological characters used to separate Pratylenchus penetrans from other species of the genus was studied in a population originating from a single gravid female. Pronounced heteromorphism was observed and characterized. About 30% of females had a crenate-tail terminus. Several shapes of stylet knobs were characterized; 50% of them were anteriorly flattened to indented. The outer margin of the cephalic framework extended into the body from one-half to two annules. The shape of the spermatheca varied from round to oval. A fifth lateral line was observed in many specimens. Environmental factors, and particularly the host plant, influenced such morphometric characters as body length, width, esophagus length, stylet length, V value, a and b' ratios, as well as qualitative characters such as tail terminus, growth of ovary, and shape of median bulb. Nematodes reared on pea and cabbage had a higher percentage of females with a crenate-tail terminus than those from tomato, rye, beet, and alfalfa callus culture. Nematodes from peas were longer and wider; they often had gonads that extended to esophagi, but they had shorter esophagi amt stylets than those from callus culture. Populations from different geographical locations also exhibited variahility in morphological characters, as did the Cornell population. The validity of many characters used in species identification is discussed, and the possibility that other related Pratylenchus species are conspecific with P. penetrans is suggested.

Sex expression and tail morphology of female progenies of smooth-tail and crenate-tail females of Pratylenchus penetrans.

An analysis of the offspring of single smooth- and crenate-tail females of Pratylenchus penetrans indicated the existence of progenies containing only males or females. Of the 80 progenies analyzed, 46 contained females with smooth and crenate tails. In general, regardless of the mother's tail type, most females possessed crenate tails, although more crenate-tail females originated from a crenate-tail female than from a smooth-tail female. Twenty-three progenies contained only females with crenate tails, most of them originating from crenate-tail females. One progeny originating from a smooth-tail female contained only females with smooth tails. No simple interpretation of the inheritance of tail type could be attempted because selection pressure favored females with crenate tails when P. penetrans was reared on Wando pea plants.

Pathogenicity of Meloidogyne hapla to Lettuce as Affected by Inoculum Level, Plant Age at Inoculation and Temperature.

Pathogenicity of Meloidogyne hapla to lettuce was influenced by inoculum level, age of plant at inoculation and temperature. Top weight of 'Minetto' lettuce was reduced 32% when 2-week-old lettuce plants were each inoculated with five egg masses. Higher inoculum levels did not further decrease top weight significantly. Inoculation at seeding reduced top growth more than inoculation of 1-, 2- or 3-week-old seedlings. M. hapla reduced growth more at the intermediate (21.1 C night and 26.7 C day), than at the low (15.5 C night and 21.1 C day) or high (26.7 C night and 32.2 C day), temperature regimes.

Meloidogyne hapla in Organic Soil: Effects of Environment on Hatch, Movement and Root Invasion.

Using new techniques, hatch and movement of Meloidogyne hapla and nematode invasion o f lettuce roots growing in organic soil were studied under controlled soil conditions of temperature, moisture, O and CO. When O levels of 2.7, 5, 10, 21 and 40% with CO maintained at 0.03% were used, O below 21% or at 40% reduced nematode activities compared with those at 21%. When CO levels of 0.03, 0.33, 2.8, 10 and 30% with O maintained at 21% were used, all levels above 0.03% CO resulted in less activity than at 0.03% except for more invasion at 0.33% than at 0.03%. Results suggested M. hapla was tolerant of CO below 10% but adversely affected by 30% CO. Effect of O was influenced by the level of CO present. No larvae invaded roots at 3.2% O and 18.6% CO but hatch and movement occurred. Night and day temperatures of 21.1 and 26.7 C were more favorable for movement and invasion than 15.5 and 21.1 C, 26.7 and 32.2 C or 26.7 and 32.2 C. Optimum moisture for movement was 80 cm suction and for invasion was 100 cm.

Effect of Temperature on Growth, Development and Reproduction of Meloidogyne hapla in Lettuce.

Temperature was an important factor in growth, development and reproduction of Meloidogyne hapla in lettuce. Growth, as measured by increase in diameter of females, was not appreciably different at the intermediate (21.1 C night and 26.7 C day) and high (26.7 C night and 32.2 C day) temperature regimes, but was considerably less at the low temperature regime (15.5 C night and 21.1 C day) than at the two higher temperature regimes. Second-stage female larvae developed into adults 14 days after inoculation at the high, 18 days at the intermediate and 34 days at the low temperature regime. Eggs were observed 20 days after inoculation at the high, 26 days at the intermediate and 54 days at the low temperature regime. Number of eggs and larvae after 6 weeks was greater at the high than at the intermediate temperature regime and no eggs or larvae occurred at the low temperature regime during the observed 6 weeks.

Pectinases in Aqueous Extracts of Ditylenchus dipsaci.

Aqueous extracts of a population of Ditylenchus dipsaci isolated from onion and maintained monoxenically on onion callus contained endo-polygalacturonase (endo-PG) and endo-pectinmethyltranseliminase (endo-PMTE). In viscometric tests pH 4.2 and 4.0 were optimal for degradation of sodium polypectate and pectin N.F., respectively, by endo-PG. Endo-PMTE reduced viscosity of pectin N.F. optimally at pH 8.5 or above. Activity was dependent on CaCl. Pectinmethylesterase activity was not detected in water, NaCl, or sucrose extracts of these nematodes. The extracts macerated potato tuber tissue, onion cotyledonary tissue, and strips of onion epidermis from the ventral surface of onion bulb scales at pH 4.2, 5.3, and 6.2. Pectin could not be localized with hydroxylamine-ferric chloride reagent in macerated tissues treated for 24 hr with active extract.

A Comparison of Pectinases from Ditylenchus dipsaci and Allium cepa Callus Tissue.

Ground and whole Ditylenchus dipsaci maintained on onion callus contain no culturable micro-organisms when tested with five check media. Healthy onion callus does not produce pectolytic enzymes. Pectolytic enzymes are present in infected callus. These enzymes are, however, associated with resident nematodes and not host tissues. These results suggest that D. dipsaci is the actual source of the endo-polygalacturonase and endo-pectinmethyltrans-eliminase extracted from them.

Thermotactic response of some plant parasitic nematodes.

Attraction of Ditylenchus dipsaci and Pratylenchus penetrans to a temperature gradient was tested. Heating wires, infrared radiations and germinating alfalfa seeds were used to create a temperature gradient as small as 0.033 C/cm in agar. P. penetrans, D. dipsaci, and Tylenchorhynchus claytoni responded to a temperature gradient of 0.033 C over a 4-cm distance from the heat source. Trichodorus christiei and Xiphinema arnericanum showed no response. Individuals of P. penetrans oriented their heads towards the heat source and moved directly towards it from a 1-cm distance within 10 rain. When the heat was turned off the nematodes dispersed, but when the heat was turned on again, they reassembled. Heat from germinating alfalfa seeds, in the absence of CO, attracted P. penetrans. Carbon dioxide emanating from germinating alfalfa seeds failed to attract them in the absence of heat, even after 24 hr.