Abstract
Thorough knowledge of the germination behavior of weed species could aid in the development of effective weed control practices, especially when glyphosate resistance is involved. A study was conducted using two glyphosate-resistant (GR) (SGW2 and CP2) and two glyphosate-susceptible (GS) (Ch and SGM2) populations of Chloris virgata, an emerging and troublesome weed species of Australian farming systems, to evaluate their germination response to different alternating temperature (15/5, 25/15 and 35/25°C with 12 h/12 h light/dark photoperiod) and moisture stress regimes (0, -0.1, -0.2, -0.4, -0.8 and -1.6 MPa). These temperature regimes represent temperatures occurring throughout the year in the eastern grain region of Australia. Seeds germinated in all the temperature regimes with no clear indication of optimum thermal conditions for the GR and GS populations. All populations exhibited considerable germination at the lowest alternating temperature regime 15/5°C (61%, 87%, 49%, and 47% for Ch, SGM2, SGW2, and CP2, respectively), demonstrating the ability of C. virgata to germinate in winter months despite being a summer annual. Seed germination of all populations was inhibited at -0.8 and -1.6 MPa osmotic potential at two alternating temperature regimes (15/5 and 35/25°C); however, some seeds germinated at 25/15°C at -0.8 MPa osmotic potential, indicating the ability of C. virgata to germinate in arid regions and drought conditions. Three biological parameters (T10: incubation period required to reach 10% germination; T50: incubation period required to reach 50% germination; and T90: incubation period required to reach 90% germination) suggested late water imbibition with increasing moisture stress levels. The GR population SGW2 exhibited a distinctive pattern in T10, T50, and T90, possessing delayed germination behaviour and thus demonstrating an escape mechanism against pre-plating weed management practices. Knowledge gained from this study will help in developing site-specific and multi-tactic weed control protocols.
Highlights
Chloris virgata Sw. is a summer annual species of Poaceae family that is considered a troublesome weed species across the tropics of the world
The major aim of this study was to enhance the scant knowledge about C. virgata germination in response to different temperature regimes and moisture stress regimes, whether this differs between GR and GS populations, and different water stress adaptability of GR and GS populations under different alternating temperature regimes
final cumulative germination (FCG) at 0 MPa was 61% and 87% for Ch and SGM2, respectively, at 15/5 ̊C; 65% and 79% for Ch and SGM2, respectively, at 25/15 ̊C; and 48% and 74% for Ch and SGM2, respectively, at 35/25 ̊C (Table 1). These results suggest that the FCG of the GR populations (SGW2 and CP2) was lower compared to the GS populations (Ch and SGM2) (p = 0.001)
Summary
Chloris virgata Sw. is a summer annual species of Poaceae family that is considered a troublesome weed species across the tropics of the world It possesses a C4 photosynthesis mechanism, monocotyledon seed structure, and is commonly referred to by many names depending on the region, such as Feathertop Rhodes grass in Australia; feathered finger grass, feathered windmill grass, and feathered Chloris in the United States; and oldland grass and sweetgrass in southeast Asia [1]. The seeds of C. virgata are comparatively smaller than other weed species, aerodynamic in shape, lightweight, and exhibit two protruded trichomes (hairs) These morphological structures aid seeds in dispersal from one ecosystem to another and increase C. virgata’s potential invasiveness [4]. The two protruded trichomes could help C. virgata seeds in sticking to agricultural machinery and labors, reducing the energy required for dispersal
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