Growth and yield of barley in relation to grasshopper feeding damage

Abstract

. 2008. Growth and yield of barley in relation to grasshopper feeding damage. Can. J. Plant Sci. 88: 219Á227. Grasshoppers are common pests of barley (Hordeum vulgare L.) in subarctic Alaska and cause substantial crop loss during outbreaks, but there is little information about the growth response of barley to grasshopper feeding damage. In two growth chamber experiments, we studied the effect of four densities (0, 1, 2, and 3 pot Á1 , equivalent to 0, 25, 50 and 75 grasshoppers m Á2) of grasshoppers (Melanoplus sanguinipes F.) on the above-and below-ground growth of barley (eight plants per pot). Plants were exposed to grasshoppers beginning in the 3rd to 4th leaf stage (exp. 1) and in 1st to 2nd leaf stage (exp. 2). Plants were harvested and growth variables were measured shortly after anthesis and at maturity. Generally, the reduction in above-ground dry matter, at the highest density was 29 and 47% for exp. 1 and exp. 2, respectively. Effects of grasshoppers on below-ground growth (dry matter and surface area of roots) was less consistent than on above-ground variables; however, at the highest grasshopper density in exp. 2, dry matter and surface area of roots were reduced by about 40Á53%. Grain yield (pooled over experiments) decreased by 19 and 36% for grasshopper densities of 2 and 3 pot Á1 , respectively. Most of the yield loss was accounted for by reduced seed weights, while protein content per seed remained nearly constant. The proportion of total above-ground dry matter represented in harvested grain and root:shoot ratios were not affected by grasshopper feeding. These results provide greater understanding of plant responses to insect feeding damage and will lead to more accurate estimates of economic injury levels. ) dans les zones subarctiques de l'Alaska. Durant les infestations, elles causent des pertes substantielles aux cultures, mais on sait peu de choses sur la re´action de l'orge a`de tels dommages au niveau de la croissance. Les auteurs ont e´tudie´l'incidence de quatre densite´s (0, 1, 2 et 3 insectes par pot, soit l'e´quivalent de 0, 25, 50 et 75 par m 2 ) de sauterelles (Melanoplus sanguinipes F.) sur la croissance des organes ae´riens et souterrains de l'orge (huit plants par pot), lors de deux expe´riences en chambre de croissance. Ils ont re´colte´les plants et mesure´les variables de la croissance peu apre`s l'anthe`se ainsi qu'a`maturite´. Dans l'ensemble, la re´duction de la concentration de matie`re se`che dans les organes ae´riens s'est respectivement e´tablie a`29 % et a`47 % lors de la premie`re et de la deuxie`me expe´rience, a`la densite´la plus e´leve´e des ravageurs. Les sauterelles ont une incidence moins cohe´rente sur la croissance des organes souterrains (concentration de matie`re se`che et superficie des racines) que sur la croissance des organes ae´riens. Ne´anmoins, lors de la deuxie`me expe´rience, a`la densite´de sauterelles la plus e´leve´e, les auteurs ont note´une baisse de 40 % a`53 % de la concentration de matie`re se`che et de la superficie des racines. Le ren...