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Received: 8 February 2018 Revised: 28 September 2018 Accepted: 4 October 2018 DOI: 10.1111/jac.12312
H E AT S T R E S S
Australian rice varieties vary in grain yield response to heat stress during reproductive and grain filling stages Fawad Ali1 | Daniel L.E. Waters2 | Ben Ovenden3 | Peter Bundock1 | Carolyn A. Raymond1 | Terry J. Rose1 1 Southern Cross Plant Science, Southern Cross University, Lismore, New South Wales, Australia 2
Abstract Climate change may lead to an increase in both day and night time temperatures in
ARC ITTC for Functional Grains, Charles Sturt University, Wagga Wagga, New South Wales, Australia
rice (Oryza sativa L) growing regions, but the impact of such temperature increases on
3
NSW Department of Primary Industries, Yanco Agricultural Institute, Yanco, New South Wales, Australia
yield response of eleven Australian rice varieties including long, medium and short
Correspondence Terry J. Rose, Southern Cross Plant Science, Southern Cross University, Lismore, NSW, Australia. Email:
[email protected]
three stages: from panicle exertion to anthesis (PE), from anthesis to 10 days after
yields of Australian rice varieties is not known. We evaluated the biomass and grain grain types, and the Californian cultivar M205, to heat stress during the reproductive phase and grain filling stages. Heat stress (day/night = 35/25°C) was applied at one of anthesis (EGF) and from 10–20 days after anthesis (LGF) periods after which the effect on biomass and grain yield was compared to control plants. When heat stress was applied at PE and early grain filling stages, mean grain yield losses across rice varieties were 83% and 53%, respectively, though significant genotype × heat stress treatment interactions were observed. Notably, three varieties—YRM 67, Koshihikari and Opus—appeared to possess greater tolerance to heat stress at these growth stages. A significant genotype × heat stress treatment interaction was also observed in the LGF treatment, where significant yield reductions were only observed in Opus (21% loss) and YRM 67 (25% loss). A lack of effect of heat stress on total grain yield in most varieties at late grain filling appeared to be due to late tiller grain yields which were either unaffected by the heat stress or increased significantly compared to control plants. While genetic variation for tolerance to heat stress across the three growth stages was observed, there was no rice genotype that was consistently tolerant (in terms of yield under stress) across all three heat stress treatments. In the absence of a genotype that showed broad heat stress tolerance during reproductive growth, we suggest screening of a wider pool of more diverse rice germplasm is warranted.
1 | I NTRO D U C TI O N
crop cultivated in over 100 countries, and the grain is consumed by 3 billion people worldwide (Wassmann et al., 2009). Any impact of
Mean global temperatures are predicted to increase by 2–3°C over
climate change on the yields and quality of rice will have critical ram-
the next 30–50 years as a result of climate change (IPCC, 2007).
ifications for world food security.
Heat events are predicted to become more intense, with negative
Rice plants are sensitive to high temperature stress during game-
consequences for crop growth and grain yields (Li et al., 2015; Wang,
togenesis (microspore and megaspore formation). At around 5–8 days
Martre et al., 2017). Rice (Oryza sativa L.) is a highly thermosensitive
before booting, heat stress can significantly affect spikelet fertility
J Agro Crop Sci. 2018;1–9.
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ALI et al.
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and reduce grain yield (Jagadish, Craufurd, & Wheeler, 2007; Jagadish
soil in each pot at rates roughly equivalent to 100 kg N/ha, 30 kg P/
et al., 2010; Yoshida, 1981). For example, high day temperatures up
ha and 30 kg K/ha, on a pot soil surface area basis before soils were
to 38°C decreased grain yields in elite rice varieties by 7%–10% in a
inundated with tap water.
controlled environment study (Madan et al., 2012). Identifying genetic sources of tolerance to heat stress to enable breeding of rice varieties that can maintain yield and quality with
2.3 | Plant material
increasing global temperatures is an important step towards main-
Seeds of eleven rice varieties and one cultivar were obtained from
taining future food security (Fitzgerald & Resurreccion, 2009; Peng
the Australian rice breeding programme, Yanco Agriculture Institute,
et al., 2004). Several studies have sought to identify rice varieties
Leeton (2705), New South Wales, Australia. The genetic material
tolerant to heat stress, particularly at booting and anthesis stages,
consisted of 11 Australian rice varieties including short grain (Opus
and a wide range of genotypic tolerance (in terms of yield reduc-
and Koshihikari), medium grain (Baru, YRM66, YRM67, Amaroo),
tions) has been reported (Table 1). Subsequent studies have mapped
long-medium grain (Reiziq) and long grain (Topaz, Kyeema, Doongara
quantitative trait loci (QTLs) associated with the tolerance to heat
and Langi), and the Californian cultivar M205 (medium grain).
stress; however, many of the QTLs mapped were identified in indica rice varieties, or rice varieties with unknown grain quality. The Australian rice industry focusses on producing premium qual-
2.4 | Plant growth
ity rice for high-end export markets using japonica-based varieties,
Seeds were germinated on a mesh floating above nutrient solution
and as such, any introgression of heat tolerance traits from indica va-
containing 1 mM calcium (Ca) and 36 μM iron (Fe) in a 20 L tray.
rieties would require extensive backcrossing to restore yield and grain
After 7 days, the nutrient solution was replaced with full strength
quality traits (Xu & Jauhar, 2014) under changing climate. Australian
Yoshida solution (Yoshida, Forno, Cock, & Gomez, 1976). At 16 days
rice breeding efforts may be simplified if variation for heat tolerance
after sowing (DAS), seedlings were transplanted into pots containing
could be found from within existing Australian rice varieties.
soil (see above) with three evenly sized seedlings planted in each
The present study aimed to inform selection for heat tolerance in
pot. Plants were then grown under controlled conditions (tempera-
temperate japonica rice breeding programmes and specifically aimed
ture day/night 28/21°C; 12 hr/12 hr) in a glasshouse at Wollongbar
to resolve: (a) which reproductive growth stages are the most sen-
Primary Industries Institute, Wollongbar (2477), New South Wales,
sitive (in terms of grain yield reductions) to heat stress in Australian
Australia. Temperature in the glasshouse was maintained day/night
rice varieties; (b) whether variation exists for tolerance to heat stress
using a reverse cycle air conditioner and fans to circulate air continu-
during reproductive growth and grain filling stages among Australian
ously. The air temperature was measured every 5 min with an EL-
rice varieties and (c) whether the grain yield response of early tillers
USB-1 temperature data logger (Microdaq.com; Figure 1).
to heat stress differs from that of late tillers.
2 | M ATE R I A L S A N D M E TH O DS 2.1 | Trial design
2.5 | Imposition of heat stress treatments Heat stress day/night (35/25°C; 12 hr/12 hr) was imposed on rice plants at three growth stages: from panicle exertion to anthesis, early grain filling and late grain filling (Figure 2). However, because pots
A pot trial was conducted to investigate the impact of heat stress
were transferred to neighbouring bays to receive the temperature
during reproductive growth and grain filling stages—panicle exertion
stress treatment individually owing to minor differences in plant phe-
to anthesis, early grain filling and late grain filling on the grain yields
nological development in pots from the same treatment, it is possible
of rice varieties used as parents in the Australian rice breeding pro-
that some of the observed differences are a result of the interaction
gramme. Each rice cultivar (12) × treatment (three heat stress treat-
between the heat stress and the external weather conditions during
ments and a control) combination was replicated three times, and
the heat stress period when 50% of spikelets on a panicle had flow-
pots were laid out in a completely randomised design.
ered (Julia, Wissuwa, Kretzschmar, Jeong, & Rose, 2016). Early grain filling (EGF) was defined as the period from anthesis until 10 days
2.2 | Soil characteristics
after anthesis (DAA) while late grain filling (LGF) was defined as the period between 10 DAA to 20 DAA. Day temperatures ran from 7
Soil was collected from the 0–150 mm layer of a Brown Dermosol
a.m. to 6.59 p.m., while night temperatures were imposed from 7 p.m.
(Isbell, 1996) at Southern Cross University’s Brookside field site
to 6.59 a.m. Time of panicle emergence was recorded for each pot to
(28°49′3.74″S, 153°18′21.49″E). Briefly, the soil has a pH of 5.2 (1:5
ensure all pots received the appropriate length of treatment.
water extract), total carbon 2.2%, Bray 1 P 0.6 mg/kg and CEC 13.6
Individual pots were moved to a neighbouring glasshouse bay
cmol+/kg. A detailed description of the soil is given in Rose, Raymond,
with day/night temperatures of 35/25°C at the appropriate time for
Bloomfield, and King (2015). Soil was passed through a 2 mm sieve,
each treatment. After 10 consecutive days of heat stress, the pots
and 8 kg per pot air-dry soil was added to 10 L (246-mm-diameter),
were returned to the control glasshouse bay where day/night tem-
non-draining black plastic pots. Basal fertiliser was mixed into the
peratures were 28/21°C.
Heat stress applied at up to 10–12 days after anthesis and imposed between 10:00 a.m. and 03:00 p.m.
38°C
27°C, 32°C
35°C, 38°C
>35°C
38°C
35°C, 38°C
Absolute spikelet fertility
Grain yield
Seed set
Grain yield
Spikelet fertility
Spikelet fertility
Heat stress applied between 07:30 a.m. and 03:30 p.m. on main tillers
Heat stress applied at up to 10-12 days after anthesis and imposed for 6 hr a day between 10:00 a.m. and 03:00 p.m.
Post-heading heat stress
Heat stress applied at up to 5 days after anthesis and imposed between 10:00 a.m. and 03:00 p.m.
High night-time temperature stress applied 20 days after emergence until maturity, ran from 08:00 pm to 06:00 am
Heat stress applied at up to 10–12 days after anthesis and imposed for 2–6 hr between 10:00 a.m. and 03:00 p.m.
30°C, 35°C & 38°C
Spikelet fertility
Heat stress applied at up to 10–12 days after anthesis. Plants were subjected to heat stress for 1, 2, 4 and 6 hr centred on the peak flowering time 11:00 a.m. to 11:30 a.m.
Duration of stress
30°C, 35°C & 38°C
Temperature stress
Spikelet fertility
Trait
240 accessions
(Pradhan et al., 2016)
(Shi, Ishimaru et al., 2015)
18 genotypes
Tolerant genotypes (20% spikelet sterility), moderate tolerant (50% spikelet sterility) susceptible genotypes (90% spikelet sterility) 10%–90% spikelet sterility
(Shi, Ishimaru, Gannaban, Oane, & Jagadish, 2015)
Data collected from 228 weather stations in China
(Madan et al., 2012)
(Mohammed & Tarpley, 2011)
One (1), Cocodrie, a US tropical japonica cultivar Three (3)
(Jagadish et al., 2010)
(Jagadish, Craufurd, & Wheeler, 2008)
(Jagadish et al., 2007)
Reference
181 RILs
18 genotypes (japonica, indica and glaberrima)
Two (2) IR-6 4 and Azucena
No. of genotypes
Rice cultivars of China (3.9–7.4% yield losses)
Tolerant genotype N22 (seed set 65%), susceptible genotypes (IR-6 4 and Hybrid IR75217H) seed set 10-20%
Decreased the grain yield and grain weight significantly (% reduction was not mentioned)
90%–93% spikelet sterility
24%–90% spikelet sterility
20%–70% spikelet sterility
Tolerance range
TA B L E 1 The range of heat stress tolerance previously identified and compared to present study data
When heat stress (35/25°C; day/night, 12 hr/12 hr) was applied at PE and EGF (anthesis to 10 DAF) stages, mean grain yield losses across rice varieties were 53%–83%. Medium grain (YRM 67) and short grain (Koshihikari and Opus) genotypes had greater tolerance to heat stress at PE and EGF compared to long grain genotypes. While during LGF (10–20 DAF) ≤25% grain yield losses were observed. The cultivars had no consistent pattern of grain yield loss under heat stress applied at PE, EGF and LGF
Present study
ALI et al. 3
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ALI et al.
Temperature (oC)
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Date (when heat stress was applied)
F I G U R E 1 The air temperature (day/night; 35/25°C; 12 hr/12 hr) inside the glasshouse bay during each treatment period (PE, EGF and LGF) for 10 consecutive days, imposed on twelve rice genotypes
Treatment 1 (when 50 % of the head had just emerged from the boot up to anthesis)
Panicle exertion
Treatment 2 (anthesis to 10 days a er anthesis)
Anthesis (50 % of the tillers had flowered)
Treatment 3 (10 days-to-20 days a er anthesis)
Early grain filling (10 days after anthesis)
Late grain filling (20 days after anthesis)
F I G U R E 2 Reproductive and grain filling stages when heat stress treatment (day/night = 35/25°C) was applied in this study
2.6 | Measurements
tagged and recorded as late tillers and main tillers referred as early tillers. As noted by Yoshida (1981), some varieties may
Crop phenology (time of booting, anthesis and maturity)
initiate panicle primordia in main tillers before the maximum
was recorded for each cultivar. Tillers that flowered be-
number of tillers is produced, and consequently heading can
yond 7 days after 50% of the main tillers had flowered were
be staggered as the later tillers may produce panicles. Plants
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ALI et al.
were har vested at maturity when grain moisture content
greatest expedition of flowering was observed in YRM67 (−6 days)
was 18%–22% (using a KET T moisture metre: PM 650 KET T
and flowering time in Doongara and Baru remained unchanged
Japan). Early and late tillers were separated at har vest, and
(Table 2).
grain was threshed manually. Grain biomass was expressed at 14% moisture, while straw was dried at 40°C for 5 days and weighed. The total plant biomass (g) was calculated as
3.2 | Grain yield
the sum of straw biomass (g) and grain yield measured in g at
There was a significant effect of heat stress treatment and genotype
14% moisture. Early tiller biomass was calculated by adding
on total grain yield, early tiller grain yield and late tiller grain yield
early tiller grain yield (g) and their straw weight (g). Similarly,
(p
