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Perennial grains have been proposed to stabilise fragile lands while contributing grain and grazing in mixed farming systems. Genotype by environment (GxE) interactions for grain yield were investigated in 22 perennial rice ( Oryza sativa L./ Oryza longistaminata ) derivatives over four successive growing seasons at three sites in Yunnan in southern China and one site in Lao PDR. The GxE interaction accounted for 25.7% of the total sum of squares, with environment and genotype responsible for 57.4% and 16.9%, respectively. Cluster analysis identified seven environment and six genotype groups, which accounted for 55.6% of the GxE sum of squares. Principal component axes 1, 2 and 3 accounted for 42.3%, 19.1% and 16.5% of the GxE-SS, respectively, with PCA1 indicating yield potential, PCA2 delay in phenology under environmental stress, and PCA3 ratoon percentage. Environment groups differed in mean temperature, whether dry season or wet season, and occurrence of environmental stresses, such as periods of low minimum temperature or periods of rainfall deficit. Genotype groups differed in adaptation to these diverse environments. For genotype groups, G5 (PR23) was highest-yielding and broadly adapted across environments, while G1 (line 188, both 137s, both 139s, both 147s) was low-yielding and poorly adapted. Other genotype groups showed preferential adaptation: G3 (lines 60, 251, 264, Bt69, Bt71) to Simao/Dry Season (E3 and E4), G4 (lines 75, 243, 246, 249, 255) to Menglian/Wet Season (E1 and E2), G2 (line TZ) to Jing Hong 2013 (E7), and G6 (lines 56, 59, 214) to Jing Hong 2102 and Na Pok (E6 and E5). The results imply that regrowth success and maintenance of spikelet fertility over regrowth cycles are important for adaptation of perennial rice, especially to low minimum temperature at higher altitude and rainfall deficit at lower altitude, and future breeding programmes in perennial rice should address these environmental stresses. The high yield and broad adaptation of PR23 (G5) over environments makes it a prime candidate for release to stabilise fragile lands in the humid and subhumid tropics, while contributing grain and forage in mixed-farming systems. [ABSTRACT FROM AUTHOR]

• Innovated perennial rice cropping system is successful for grain food security. • Regrowth over-year of perennial rice was significantly limited by high N rate. • Scheme of N2D3 had best N effects and N profit in perennial rice cropping system. • Scheme of N2D3 are recommended for sustainable production of perennial rice. • Our empirical results may also have implications for other perennial grains. Perennial grain has been proposed to provide an effective means of ensuring both food and ecological security. The newly released cultivar of perennial rice 23 (PR23) represents a new rice production system that is based on no-tillage. Nevertheless, how perennial rice responds to this new system remains unclear. Two field experiments were conducted over four successive seasons from 2016 to 2017 in Jinghong, Yunnan Province, Southern China. Field experiment 1 showed perennial rice is an economically viable and environmentally safe cropping system compared to annual rice, and could obtain a stable and sustainable grain yield economically for successive seasons across years. In the perennial rice cropping system, N fertilizer had some negative effects on the regrowth of perennial rice. Field experiment 2 with four N rates N0, N1, N2 and N3 with 0, 120, 180 and 240 kg N ha−1, respectively and three planting densities D1, D2 and D3 with 10, 16.7 and 22.6 plants m-2, respectively on perennial rice was conducted to assess and ameliorate these negative effects of N fertilizer on the regrowth of perennial rice. The results showed that: (1) the N2D3 treatment (180 kg N ha−1 integrated with 22.6 plants m−2) resulted in a stable and high grain yield across three successive regrowth seasons (6.93 t ha−1) and optimized yield components (panicle no. m-2, spikelet no. panicle−1, grain weight) and root activity (10.81 g h−1 m-2); (2) the regrowth of perennial rice 23 was significantly limited by N fertilizer (P <0.05), and the N0D2 treatment had the best regrowth ability (97.8 %) across the three regrowth seasons; (3) additionally, the N2D3 treatment had the best N net productivity (27 kg N kg−1), profit (79 CNY kg−1) and sustainable production capacity (0.59), and could obtain more economic profit in successive perennial rice production. Perennial rice was able to be sustainably and economically produced for successive regrowth seasons across years, and the N2D3 treatment provided optimal conditions, which enhanced the regrowth rate, N productivity, economic benefit and yield potential. The use of less chemical N fertilizer and a higher planting density could enhance the sustainability of the grain yield and reduce fertilizer loss via a novel crop management scheme for perennial rice. [ABSTRACT FROM AUTHOR]

• GxE interaction was large, accounting for 37.7% of T-SS, with E 25.7% and G 33.8%. • PCA1 indicated yield potential, PCA2 yield over ratoon cycles, PCA3 ratoon percent. • Environments differed in yield potential and in performance over ratoon cycles. • Genotypes differed in yield, maturity, regrowth and performance in later ratoon cycles. • PR23 performed similarly to seasonally-replanted BN21, over up to six growth cycles. Genotype by environment (GxE) interactions for performance of 5 perennial rice genotypes (Oryza sativa L./ Oryza longistaminata) were examined relative to 1 mutant and 3 annual rice genotypes over 2–6 growth cycles at 7 locations in southern China between 2014 and 2017. Environment main effects accounted for 25.7% of the total sum of squares (SS), with genotype 33.8% and GxE 37.7%. Cluster analysis identified 6 genotype x 6 environment groups, which accounted for 77.9% of the GxE-SS. Principal component axes 1, 2 and 3 accounted for 54.7%, 25.1% and 9.4% of the GxE-SS, respectively, with PCA1 indicating yield potential, PCA2 performance over ratoon cycles, and PCA3 ratoon percentage. Environment groups differed in yield potential, which related to site favourability and whether it was low or high in the ratoon cycle. Genotype groups differed in yield potential and how well they performed in higher ratoon cycles. The medium-maturity (125 days) seasonally-replanted annual rice check BN21 was highest yielding (6.13 t ha−1). Perennial rice PR23 was high yielding and stable (5.25 t ha−1), with earlier maturity (119 days) and strong regrowth (82%). Ratooned annual rice RD23 was high yielding in original crops but poor yielding in ratoon crops, with a low ratoon percentage (16.5%). Similarly, perennial Bt71 and ratooned BN21 were high yielding in original crops and low-cycle ratoons under favourable conditions, but yielded poorly in high-cycle ratoons and less favourable conditions, with moderate regrowth (59.6%). Despite strong regrowth (77.5%), perennials 264 and Bt69 had low yield, as did perennial 139A and mutant TZ, and both these groups were late maturity. A combination of high yield potential, strong regrowth and earlier maturity resulted in higher performance of perennial rice over environments and regrowth cycles, with PR23 outstanding, and able to perform similarly to the seasonally-replanted annual check, BN21, over up to six growth cycles. Ratoon performance and trade-offs need to be examined further. [ABSTRACT FROM AUTHOR]