IJERD – International Journal of Environmental and Rural Development (2020) 11-2

Research article
erdPhysiological Variables Associated with Yield of Improved
Rice (Oryza sativa L.) Genotypes in Normal and Late
Growing Seasons
ZUN PHOO WAI*
Yezin Agricultural University, Nay Pyi Taw, Myanmar
Email: zunphoowai.yezin@gmail.com

NYO MAR HTWE
Yezin Agricultural University, Nay Pyi Taw, Myanmar

SU LATT PHYU
Yezin Agricultural University, Nay Pyi Taw, Myanmar
Received 20 January 2020

Accepted 12 December 2020(*Corresponding Author)

Abstract Genotypic selection for higher total dry weight has become a key method ofresearch and experimentation to increase grain yield. Therefore, this experiment was carriedout to determine the relationship of leaf area index (LAI) and yield and its components forten genotypes of improved rice, for normal and late growing seasons. The experiments wereconducted in the experimental fields of the Department of Plant Breeding, Physiology andEcology, Yezin Agricultural University. The study was undertaken from December 2016 toMay 2017 for testing normal growing season plants and March 2018 to July 2018 for late
growing season plants. A randomized complete block design with three replications wasused. For the relationship among all the traits tested, positive associations were found (R2 >0.5) for LAI at harvest and yield (R2 = 0.574), for panicle weight at harvest and yield (R2 =0.558), and for harvest index (HI) and yield (R2 = 0.61). The study showed that yields increase
along with an increase in LAI and panicle weight, for the improved rice genotypes that weretested. There was a positive and significant correlation found between LAI at heading stage
and percent of filled grains in normal season, and LAI at heading and number of panicles permeter square in late season. In late season, the correlation between LAI at harvesting stageand yield was significant; HI was also significantly correlated with percent of filled grains
and yield. As LAI and harvest index contribute to yield and yield component characters,
breeders may successfully attempt to boost potential yields by increasing growth traits suchas plant foliar surface and harvest index.
Keywords yield, LAI, correlation

INTRODUCTION
Rice is the most important food crop in the world and serves as a staple food for more than one thirdof the world’s population (Singh and Singh, 2008). About 90% of the world’ rice growing area is on
the Asian continent (Salim et al., 2003). It is estimated, farmers in the world need to produce about
60% more rice than at present to meet the food demands of the world population expected by 2025
(Thakur et al., 2011).
In Myanmar, rice is a staple food and is cultivated in an area of 7.28 million hectares. Total
production is 28.09 million metric tons, giving a yield of 3.92 ton/ha (Department of Planning,
Ministry of Agriculture, Livestock and Irrigation, 2018). Rice makes up 33 % of total area cropped
with 84% (6,474,970 ha) of rice grown during monsoon and 16% (1,214,056 ha) grown during
summer (Sein, 2014). Okamoto (2004) affirms that rice production is very important for both theeconomic livelihood and food security for the population of Myanmar.
Increases in rice production have mainly relied on the expansion of the area of cultivable land
used to grow rice, and increases in yield per unit area (Evans, 1993). Climate change and urbanizationⒸ ISERD

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can result in decreases in rice cropping areas. Therefore, the increase of yield per unit area has
become the focus to achieve increases in production. The grain yield of rice is a complex trait,
controlled by many genes and highly affected by the environment (Jennings et al., 1979). Grain yieldis also related to other characteristics, such as plant type, growth duration, and yield components(Yoshida, 1981). In comparing semi-dwarf and traditional rice cultivars, the increase in harvest index
is the contributing factor improving yield potential, rather than any increase in production of biomass(Takeda et al., 1983; Evans et al., 1984). However, modern cereal breeding programs have provided
evidence of the possibility of boosting grain yields by selecting genotypes exhibiting higher biomass
production (Boukerrou and Rasmusson, 1990; Damisch and Wiberg, 1991). The efficiency withwhich dry matter is accumulated and allocated to harvestable organs, the grains in rice, determines
the size of yield components and final yield (Fageria et al., 2006).
There are two rice growing seasons in Myanmar; summer and monsoon or dry and wet. Thesummer (dry) rice growing season is from December to May and the monsoon season (wet) fromJune to November. Sometimes summer rice growing is delayed because of labour scarcities, delaysin obtaining irrigation water or due to a late harvesting time for the previous crop.
OBJECTIVE
The aim of this research is to determine the relationship of LAI and yield, and yield related traits ofimproved rice genotypes, under normal and late growing seasons.
MATERIALS AND METHOD
The experiment was carried out in the experimental fields of the Department of Plant Breeding,Physiology and Ecology, Yezin Agricultural University from December 2016 to May 2017 fornormal season rice and March 2018 to July 2018 for late growing rice. Experimental field is locatedat longitude 19º 10′ and latitude 96º 07′ E with the elevation of 102 meters (m) above sea level.
Ten improved rice genotypes which were preliminary selected based on agronomic traits and yield,
were grown and yield estimated (Table 1) by using randomized complete block design with threereplications. Each plot was (4m × 4m) with a spacing of 20cm × 20cm. Each genotype was plantedwith 20 rows, and 20 plants per row (total 400 plants per plot). Twenty-one-day-old seedlings weretransplanted with one seedling per hill. Other agronomic practices were followed as required by using
recommended cultural practices.
Table 1 List of tested improved rice genotypes in this studyNo.
12345678910

Improved Genotype
YAU- 1201-1-2-1
YAU-1201-202-1-2
YAU-1214-183-3-1-1-1-1
YAU-1214-183-35-1-1-1-1
YAU-1215-S-S-S-40-2-1
YAU-1215-S-S-S-41-1-1
YAU-1211-116-3-4
YAU-1211-71-1-1
YAU-1201-151-1-1
YAU-1201-151-1-3

In this study, LAI and dry weight were measured at heading stage and at harvesting stage.
Heading stage was defined as the time when the main stem panicle had emerged and the harvestingstage was defined as the stage of the plants’ physiological maturity. Two rows in border areas wereleft out of the sample collected to avoid the border effect. Three representative hills (hills with a meanvalue of tillers per hill) from each plot were sampled for the determination of dry weight. All plant
samples were separated into green leaf blades (leaf), culm plus sheath (stem), and panicles. AllⒸ ISERD

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samples were oven-dried at 80°C for 72 hours to obtain a constant weight. At the time of harvest,
five representative hills were selected to measure yield and yield component traits. The weight offilled spikelets was adjusted for a moisture content of 14%. Leaf area index (LAI) was calculated as
the ratio of the sum of the leaf area of all leaves to the ground area of the field where the leaves had
been collected (Watson, 1947).
LAI=

Sum of the leaf area of all leaves
Ground area of field where the leaves have been collected

Yield per plant (g)=1000 grains weightFilled grain %Spikelet number/paniclePanicle number
1000100

The data were analyzed with Microsoft Excel (2007) and correlation analysis was also
performed by using Statistical Tool for Agricultural Research (STAR) 2.0.1 (2014).
RESULTS AND DISCUSSION
Temperature regimes were different during vegetative, reproductive and ripening stages during two
growing seasons (Table 2).
Table 2 Average of daily temperature and total rainfall during different growth stages of rice
Daily temperature

Daily temperature

Daily maximum(°C) during NS(°C) during LS

temperature ≥35°Cmax

minmaxmin

NSLS

NSLS

Vegetative

35.2

18.5

37.3

22.9

5089

44311

Reproductive

37.4

24.4

31.8

24.9

241

58264

Ripening

38.4

26.2

31.5

24.7

28093272

Growth stage

Total rainfall(mm)Source: Weather Station of Department of Agricultural Research, Yezin. NS=Normal Season, LS=Late SeasonCorrelations between physiological variables and yield and yield components for improved rice
genotypes in both NS and LS are showed in Table 3. In NS, there was no significant correlation
between the variables except LAI at heading and percentage of filled grain. It could be suggested
that percentage filled grain correlates with optimum LAI at heading. For LS crops, LAI at heading
was positively and significantly correlated with the number of panicles per meter square. Also, filledgrains percentage was positively and significantly correlated with harvest index (HI). LAI atharvesting stage, and harvest index (HI) were positively and significantly correlated with yield/m2.
A positive correlation between LAI and yield has been reported in the literature (Xie et al., 2011;
Moraditochaee et al., 2014). An increase in harvest index results in an increase in grain yield that
produces heavier grain in improved rice cultivars (Kiniry et al., 2001). Yield/m2 is demonstrably
affected by LAI and HI.
Regression analysis showed that yield/m2 is associated with dry weight at heading stage in LSwith an R2 of 0.027 though this relationship is relatively weak in NS (R2=0.038) (Fig. 1). The
relationship between yield and dry weight at harvesting stage is associated in both NS and LS with
R2s of 0.154 and 0.054 respectively (Fig. 2) . Van der Werf (1996) stated that above-ground total drymatter (ATDM) accumulation (areal total dry weight) along with its partitioning to various parts ofthe plant determined crop productivity. Under favorable growing conditions, the increased yield of
F1 hybrid rice was associated with increased total dry weight (Song et al., 1990; Yamauchi, 1994).
Yield/m2 was positively related with HI in both seasons and this was a strong relationship with an R2of 0.61 (Fig. 3). Increasing the harvest index and dry weight can achieve an increase in grain yield.
An association between yield/m2 and panicle weight in both growing seasons (Fig. 4) was foundand there was a moderate relationship with an R2 of 0.558 in LS. Panicle weight is positively relatedⒸ ISERD

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to increased dry weight from heading to harvesting with an R2 of 0.223 in NS and R2 of 0.175 for LS(Fig. 5). Weng et al. (1982) reported a similar result. The result showed that yield can be increased
with increased dry weight through the increase of panicle weight.
It was found that yield/m2 was positively related with LAI at heading stage in both NS and LS(Fig. 6). This indicates that an increase in LAI at heading stage results in an increase in yield. In NS,
yield had no relationship to LAI at harvesting stage but there was positive association of yield withLAI at harvesting stage with an R2 of 0.574 (Fig. 7) for LS. Yield/m2 was positively related withdecreased LAI from heading to the harvesting stage with an R2 of 0.141 in NS, but there was anegative association for LS (Fig. 8). Moradpour et al. (2013) stated that a strong relationship between
yield and LAI was observed. An increase in LAI at harvesting stage contributes to an increased yieldfor the late season rice.

Fig. 1 Relationship between yield/m2 and dryweight at heading stage in NS and LS

Fig. 2 Relationship between yield/m2 anddry weight at harvesting stage in NSand LS

Fig. 3 Relationship between yield/m2 and HI
in NS and LS

Fig. 4 Relationship between yield/m2 andpanicle dry weight in NS and LS

Fig. 5 Relationship between panicle weightand increased dry weight from heading
to harvesting in NS and LS

Fig. 6 Relationship between yield/m2 andLAI at heading stage of in NS andLSⒸ ISERD

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Fig. 7 Relationship between yield/m2 and LAI
at harvesting stage in NS and LS

Fig. 8 Relationship between yield/m2 anddecreased LAI from heading toharvesting in NS and LS

Table 3 Correlation between physiological variables and yield and yield components ofimproves rice genotypes during two seasons

No. of panicles(/m2)

No. of grains (/m2)

NS
2017

LS
2018

NS2017

LS
2018

NS
2017

LS
2018

NS
2017

LS
2018

LAI at heading

0.32830.7166*-0.4555-0.1294

0.6856*0.47940.35810.2769

LAI at harvesting-0.1478

0.13-0.54540.4476

0.55150.22310.04750.7574*

0.3966

0.5672-0.3475-0.2992

0.596

0.32380.3763-0.0752-0.47970.54740.44130.1823-0.16280.59170.19630.3822-0.2881-0.4026

0.12810.4363-0.056-0.2051

0.393

0.234

0.3093-0.5767-0.412

0.19550.1439-0.4670.1293-0.0527-0.16390.50340.16620.2456

0.06830.7413*0.33480.6840*

Yield and yield components

Decrease of LAI fromheading to harvesting
Dry weight at heading(g/m2)
Dry weight at harvesting(g/m2)
Increase of dry weight fromheading to harvesting (g/m2)
HI

Filled grains percent

Yield (g/m2)

NS= Normal growing season, LS= Late growing season

CONCLUSION
In this study, correlation analysis showed that yield and yield components correlated with LAI, dryweight and HI, especially for late growing season crops. According to regression results, yieldincreasing was influenced by the increase of HI, LAI and panicle weight, especially in late season
and panicle weight was contributed by dry weight. As yield and yield components are correlated withLAI, dry weight and HI, tall varieties of rice, susceptible to lodging rice should not be grown in thelate season and breeders should attempt to increase growth traits such as plant foliar surface and HI
in order to boost potential yields.
ACKNOWLEDGEMENTS
The authors would like give special thanks to the Japan International Cooperation Agency (JICA),
Project for Capacity Development at Yezin Agricultural University for the financial and technicalsupport given in conducting this study.

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