Phenology, fecundity and dormancy of Avena sterilis ssp. ludoviciana from plants grown under late season soil water stress

Wheat (Triticum aestivumL.) is the main winter crop in the northeastern grain region (NGR) of Australia, cultivated following no-till or minimum till coupled with stubble retention i.e. conservation agriculture (CA). On the other hand wild oat (Avena sterilisssp. ludoviciana(Durieu) Nyman)is considered the most difficult-to-control winter weed in NGR particularly after adoption of no-till CA. A variety of survival mechanisms (for example seed dormancy) are responsible for its persistence. Environmental stress, such as drought at late season is known to reduce wild oat (especially Avena fatuaL.) seed dormancy status. We hypothesize that a dry period during the seed development stage, will not only promote early shedding of seed but also reduce dormancy. These two traits would enable A. sterilisssp. ludovicianato be more persistent in no-till CA in NGR. To test this hypothesis we conducted a soil water stress experiment in a greenhouse (~23/14°C day/night)with five levels of soil moisture (100, 80, 60, 40 and 20% of soil water holding capacity of a black Vertosol soil –71% clay) during July to November 2018 in a completely randomized design with six replications. Four biotypes of A. sterilis ssp.ludovicianacoming from the NGR viz. Biloela 1: -24.35471 °S, 150.49773 °E; Biloela 2: -24.35048 °S, 150.497 °E, Toobeah: -28.36792 °S, 149.52197 °E and Jandowae: -26.66727 °S, 151.0246 °E were used inthis experiment. The soil moisture stress treatments were applied atpanicle initiation stage that continued until harvest. It was found that plants suffered with severe soil water stress matured 18 days earlier and produced less filled (30% less) and smaller (39% smaller) seeds compared with control plants. The biotypes coming from the northern NGR matured four to seven days earlier than the biotypes from the southern NGR. The germination test (conducted at constant 9°C under 12/12 hour light/dark condition for 42 days in an incubator) showed that 99% of primary seeds of the control plants were dormant compared with 67% of those that matured earlier than the control plants.Thus it is evident that the increasing frequency of dry period at seed development stage in the NGR is responsible for production of less dormant A. sterilisssp. ludovicianaseeds where no-till CA is helping to retain these seeds on the top soil. Under favourable germination conditions in the following autumn/winter season these less dormant seeds will immediately be available to re-infest the wheat cro