The wheat line with R gene Lr24 shows some chlorosis and allows a very few small rust pustules to develop. comm.) no sporulation occurs in any of these cases. Cebeda Capa ( R gene Rph 7) by a necrotic response while the wheat line carrying the R gene Lr20 gives mixed chlorotic and necrotic responses (ERL Jones, pers. Estate ( R gene Rph 3) is characterised by a chlorotic response, and of cv. To test further the generality of this effect, we examined the consequences of R gene resistance to brown rust in barley and wheat. Our previous 3 and unpublished studies of Bgh interactions indicate that expression of HR in the barley powdery mildew system has a common consequence leading to stomata becoming locked-open and unable to close in response to darkness, extreme drought or application of abscisic acid, even though plants appeared disease free. Major ( R) genes conveying race-specific disease resistance associated with a hypersensitive response (HR) are commonly deployed to control crop pathogens. Stomata in Lock-up: Paying the Penalty for the Hypersensitive Response? This would be a rather perverse form of вЂresistanceвЂ™ that is a consequence of susceptibility. Together with the premature leaf senescence associated with infection, this must limit colony growth, sporulation capacity and longevity of infections and thereby limit spread of disease. Interestingly, one consequence of this stomatal closure must be reduced photosynthesis thereby reducing the potential supply of assimilates available to the pathogens. While stomatal closure clearly did not prevent disease infection by the rusts, like Bgh, has obvious and serious implications for physiological activity mediated by stomatal movement.

1 and 2) show low g l, indicating failure of stomatal opening in light, until the epidermis was ruptured some time after infection. Although these rusts are also obligate biotrophs, they enter leaves via stomata and feed largely on mesophyll cells before rupturing the epidermis at the onset of sporulation.

In line with earlier studies of bean rust, 5 we recently found a very similar effect of infection by brown rust fungi in susceptible barley (cv. Our observations of compatible interactions confirmed earlier studies 4 showing that stomata in the vicinity of established colonies lost the ability to open in response to light, thus reducing leaf water conductance ( g l). hordei ( Bgh), 3 but as Bgh does not enter via stomata, the effect, if any, of this closure on the pathogen is not direct.Д«gh is an obligate biotroph with an ectophytic habit it penetrates only into epidermal cells to form feeding structures (haustoria) that supply the surface mycelia and reproductive structures. Our published study showed that rapid stomatal closure is also a pre-penetration response of barley to the powdery mildew fungus, Blumeria graminis f. 2 showed that bacterial pathogen-associated molecular patterns trigger rapid stomatal closure, and argued that this represents an innate mechanism of resistance against pathogens that enter via stomatal pores. Stomata balance CO 2 uptake with transpiration1 in response to physiological and environmental cues and they also respond to biotic stress including pathogen attack.

Enemy at the gates full