Antisense expression of peach mildew resistance locus O (PpMlo1) gene confers cross-species resistance to powdery mildew in Fragaria x ananassa

Powdery mildew (PM) is one of the major plant pathogens. The conventional method of PM control includes frequent use of sulfur-based fungicides adding to production costs and potential harm to the environment. PM remains a major scourge for Rosaceae crops where breeding approaches mainly resort to gene-for-gene resistance. We have tested an alternate source of PM resistance in Rosaceae. Mildew resistance locus O (MLO) has been well studied in barley due to its role in imparting broad spectrum resistance to PM. We identified PpMlo1 (Prunus persica Mlo) in peach and characterized it further to test if a similar mechanism of resistance is conserved in Rosaceae. Due to its recalcitrance in tissue culture, reverse genetic studies involving PpMloI were not feasible in peach. Therefore, Fragaria x ananassa LF9 line, a taxonomic surrogate, was used for functional analysis of PpMlo1. Agrobacterium-mediated transformation yielded transgenic strawberry plants expressing PpMlo1 in sense and antisense orientation. Antisense expression of PpMlo1 in transgenic strawberry plants conferred resistance to Fragaria-specific powdery mildew, Podosphaera macularis. Phylogenetic analysis of 208 putative Mlo gene copies from 35 plant species suggests a large number of duplications of this gene family prior to the divergence of monocots and eudicots, early in eudicot diversification. Our results indicate that the Mlo-based resistance mechanism is functional in Rosaceae, and that Fragaria can be used as a host to test mechanistic function of genes derived from related tree species. To the best of our knowledge, this work is one of the first attempts at testing the potential of using a Mlo-based resistance strategy to combat powdery mildew in Rosaceae.     

DIFFERENTIAL RESPONSES TO MAGNESIUM AND CALCIUM BY NATIVE POPULATIONS OF AGROPYRON SPICATUM

Plants of Agropyron spicatum (Pursh) Scribn. and Smith. from populations native to serpentine and nonserpentine soils were grown at varying levels of magnesium and calcium in culture solutions. The yields of plants from the two populations were different. At high Mg levels (low Ca) the yield of the serpentine population was significantly higher than that of the nonserpentine population. At low Mg the yield of the serpentine population leveled off at a Mg: Ca ratio of 1:2, while the yield of the nonserpentine population increased up to a Mg:Ca ratio of 1:8 and showed no leveling off. Chemical analyses of tissue showed that the Ca uptake of plants from the serpentine population was significantly higher than that of the nonserpentine population. In addition, the serpentine population maintained a lower Mg concentration in the shoots than the nonserpentine population at comparable Mg substrate levels. The two populations showed differences in Ca and Mg uptake efficiency and Mg/Ca, Ca + Mg/K + Na, and Ca + Mg + K + Na in the shoots. The ecotypic differentiation with respect to Mg and Ca between native populations of serpentine and nonserpentine A. spicatum does not appear to be due to any single mechanism but, rather, a combination of several possible mechanisms, i.e., differences in root morphology, uptake mechanisms, translocation of nutrients, and interactions between cations.     

A POPULATION STUDY OF AN EQUATORIAL LAND SNAIL, LIMICOLARIA MARTENSIANA (ACHATINIDAE)

Near the equator in Uganda, the herbivorous land snail, Limicolaria martensiana , occurs in well-defined populations. These populations may be very large and the snails may in places occur at exceedingly high densities. The snails breed all the year round, but with two peaks that correspond with the two annual dry seasons. They enter dispause whenever the weather is very dry. The size of adult snails seems environmentally determined and it varies in different populations : the largest snails occur on soil rich in calcium. The shells of the snails are highly variable and polymorphic in colour and pattern. In particular, there is a streaked form that occurs in all populations, and four distinct pallid "dilute" forms. The relative frequency of the forms varies markedly in different populations. Polymorphism is greatest at high population densities and the snails are all streaked where they are rare. Polymorphism can be distinguished in Pleistocene fossil populations.     

THE DEVELOPMENT OF BEHAVIOUR IN ELEUTHERODACTYLUS MARTINICENSIS (AMPHIBIA, ANURA)

In the genus Eleutherodactylus , development is wholly embryonic. Among other features of ontogeny which are thereby modified is the development of behaviour. Within the egg envelope, the embryo is largely still, but wriggles from time to time. These movements represent all that remains of the axial swimming behaviour of larval Amphibia. The embryo develops normally when removed from the envelopes, and its reactions to light touch can then be studied from day to day. In E. martinicensis , which develops from first cleavage to hatching in 13-14 days, the first movement of the legs is seen during trunk wriggles at 7 1/2 days, but a day later they can move independently. The first reaction of the leg is a slow withdrawal; at 9 1/2 days flexion is followed by a vigorous extension. By then, reflexes affecting all four limbs can be elicited.
Towards the end of embryonic life, limb movements can be maintained in continuous cycles, and the animal can then swim. When it is allowed normally to emerge from the envolopes, the juvenile toad, smaller than a house fly, can jump a distance of over a foot. These observations are discussed in relation to the ontogeny of behaviour in other vertebrates, particularly in regard to the views of G. E. Coghill.