Relative susceptibilities of eleven potato cultivars and breeders' clones toGlobodera pallida pathotype Pa 3, with a discussion of the interpretation of data from pot experiments
Curves according to the equationPf=M′ (1-e−aPi/M′) fitted well to the relations according to Seinhorst's (1993) modelPf=yeyhM(1-e−aPi/M) between initial egg densities of potato cyst nematodes (Globodera rostochiensis, G. pallida)Pi up to 5Th (Th=the tolerance limit of haulm weight) andPf at the end of the growing season (a=maximum rate of reproduction,M, M′=different theoretical maximum egg densities). Variation of estimates ofM′, due to variation of the parameters of the submodelsye andyh for the effect of weight reduction of haulms (and, therefore, of roots) on cyst production and damage to root tissue on egg production, respectively, was small enough to be ignored relative to experimental error. Therefore, ratios of values ofM′, determined in simultaneous pot experiments with different potato cultivars, are reliable measures of the relative host status of these cultivars at initial egg densitiesPi of these nematodes up to about 5Th. Variation between potato cultivars of growth reduction and damage to root tissue by the nematodes reduces the reliability of ratios of rates of relative susceptibility of these cultivars.The ratios between the maximum rates of reproduction ofG. pallida, pathotype Pa 3, on 8 out of 9 cultivars and one breeder's clone of potatoes and this rate on the susceptible cvs Bintje and Irene (relative susceptibilitiesrsa) could be considered to be equal to the ratios of maximum population densitiesM′ on these cultivars (relative susceptibilitiesrsM′) (relative susceptibilities independent of initial egg density). The latter ratios were 0.59 times the first (relative susceptibilities negatively correlated with initial egg density) in one cultivar and one breeder's clone. Relative susceptibilitiesrsa andrsM′ of the tested cultivars and breeders clones suggest the existence of continuous ranges of both relative susceptibilities between 0.50 and 0.15 with, in a great majority of cases,rsa=rsM′.
Relation between population density of potato cyst nematodes and measured degrees of susceptibility (resistance) of resistant potato cultivars and between this density and cyst content in the new generation
The degree of susceptibility (resistance) of a potato cultivar to (against) a pathotype of potato cyst nematode (Globodera rostochiensis (Woll.), G. pallida Stone) can be defined quantitatively as the ratio between the multiplication rate of this pathotype on the cultivar to be tested and that of the same number of nematodes on one or more susceptible cultivars, used as standards and grown simultaneously with the cultivar(s) to be tested. However, this ratio appeared to be density dependent in some susceptible cultivars. Also the relation between initial and final population densities (Pi and Pf) of pathotype Ro 1 on the resistant cultivars Ehud and Astarte differed considerably from that on susceptible cultivars. It could be described by the equation Pf = ya(1-qPi) (-elog q)-1, in which y = m + (1-m)zPi, a = the maximum rate of multiplication, q, z and m are constants 2.6: 1), but on resistant cultivars were unrelated (Ro 1 on cv. Ehud) or with much smaller ratios (< 1.8 : 1) (Ro 1 on cv. Astarte, Ro 2/3 on cv. Darwina).
The etiology and surgical management of tracheal collapse in calves.
The mean ages of 10 calves with tracheal collapse were 2.7 weeks at onset of clinical signs and 9.4 weeks at presentation for treatment. Inspiratory and expiratory dyspnea and stunted growth were the most common clinical signs. There were abnormalities of the cranial ribs consistent with healing fractures with redundant callus in eight lateral thoracic radiographs. Tracheal collapse in calves may result from cranial thoracic trauma during or soon after birth. Short polypropylene ring prostheses made from 60 ml syringe barrels were placed on the tracheas of four calves with cervical tracheal collapse. There were cranial rib masses in all calves and resection of the right first and second ribs was necessary in one calf to allow placement of prostheses. Dyspnea was relieved in all calves. One calf died of unrelated causes in year 3, and one calf had recurrence of clinical signs at month 5 and was euthanatized. In both calves, tracheal stenosis resulted from continued growth and infolding of the trachea within the constraints of the prostheses. One calf was alive at month 11, and one calf died of acute bronchopneumonia on day 2. Removal of tracheal prostheses in calves is recommended after 2 to 3 months if clinical signs recur.