Races of the Barley Root-Knot Nematode,Meloidogyne naasi. II. Developmental Rates

The developmental rates of the five newly designated races of Meloidogyne naasi were compared on barley, oat and sorghum. Races 1, 2, 3 and 4 developed and reproduced on both barley and oat but not on sorghum. Race 5 developed and reproduced readily on sorghum but poorly on oat. A more rapid rate of development of Race 5 on both barley and sorghum than that of other races on barley demonstrated that Race 5 has a shorter life cycle than do Races 1-4.     

Races of Ammomanes deserti in Arabia.

T he Arabian patchwork of differently-coloured races of the "Desert Lark" (see Ibis, 1936, pp. 332–4) can now be exhibited in a more definite shape than three years ago, since we have much additional material to work on.     

Races of the Barley Root-Knot Nematode,Meloidogyne naasi. I. Characterization by Host Preference

The host preferences of populations of Meloidogyne naasi from England, California, Illinois, Kentucky and Kansas were compared. Among 22 plant species tested, most were hosts for isolates of all five populations; crabgrass was added to the list of known hosts. Differential reactions of isolates on creeping bentgrass, curly dock, sorghum, and common chickweed demonstrated the existence of at least five physiological races within M. naasi. The known races are numerically designated and characterized.     

Races of the Barley Root-Knot Nematode,Meloidogyne naasi. III. Reproduction and Pathogenicity on Creeping Bentgrass

Reproduction and pathogenicity of the five known races of Meloidogyne naasi on two selections of creeping bentgrass were compared. Toronto C-15 was a host for Races 3, 4 and 5, whereas Northmoor 9 supported reproduction of all five races. Differences in susceptibility and population increase demonstrated that the races could be separated by degree of reproduction on the two selections. Root weights generally were unaffected. Based on cumulative dipping weights, all but Race 1 were pathogenic on at least one of the selections; Race 3 stunted top growth of both. Slight differences in degree of pathogenicity, associated with final populations, were not broad enough to be useful in race separation.     

Arms Races, Conflict Costs and Evolutionary Dynamics

In conflicts and fights, the winner is often determined by the difference in resource-holding potential, e.g. size, weaponry, strength (RHP). I model the evolution of RHP in a symmetric game with continuous strategies. I show that there is a convergence stable ESS level of RHP if the cost of the trait increases faster than linearly, and that this is the only solution if the cost increases fast enough with RHP. Otherwise with slowly increasing cost, the solution is a cyclically fluctuating level of RHP. It is also shown that if the cost increases linearly with RHP, the only solution to the game is neutrally stable cycles, the amplitude determined by the initial conditions. The cycles come about because in a population drawn into an arms race of RHP, individuals after a while suffer costs so high that mutants with the lowest possible armament level may invade. Copyright 1999 Academic Press.