Time of transplanting is the most important factor among all the agronomic components of yield that directly affect the yield in any crop especially in Basmati rice (Oryza sativa L.) varieties or lines [1]. Three climatic factors i.e. photoperiod sensitivity, temperature and humidity are reported to caste crucial effects in flowering of the Basmati rice lines. Pure Basmati lines only flower between specific ranges of these climatic factors. Any fluctuation in these factors during flowering time results in incomplete flowering. Likewise, during grain filling period, these factors are also of the same importance and significantly affect grain filling and yield reductions. Most of the Basmati rice cultivars are naturally bred to flower between the temperature ranges from 20°C to 25°C [2]. Pure Basmati lines twitches anthesis in the last week of September when temperature falls below 25°C and completes in flowering within first week October until the temperature falls below 20°C.

Transplanting Basmati rice too early or too late shortens or prolongs the duration of rice crop respectively from transplanting to panicle initiation causing sterility and lower milling quality. It is observed that variations in growth temperature by varying the transplantation dates caused variation in productivity and quality of rice crop [3]. Previous studies exploring the effects of temperature on kernel development by various researchers have showed that higher temperatures during the plant development stage of grain-filling result in decrease in rice kernel width and thickness and increased chalkiness [4]. However, effects of temperatures on amylose content of different rice cultivars were recorded significantly variable [5]. Too high or too low night time air temperature stresses causes reduced substrate supply to the grain endosperm, which results in slow growth of starch granules and irregular granular organization [6]. Ahmed et al. [7] showed that high temperature decreased the grain filling period from 32 days to 26 days, reducing yield by 6%.

The difference in quality aspects of milled rice is attributed to the difference in amylose and protein contents as well as due to structure of amylopectin in grains of milled rice before and after cooking [8].

Furthermore, variations in soil moisture and nutrient availability, ambient temperature and atmospheric composition also affected starch functionality [9].

Lanning et al. [10] also demonstrated that higher temperature results in increased accumulation of lipids and decreased accumulation of proteins and starch which is major component of milled rice and affect the cooking in terms of elongation after cooking, texture and stickiness. Liang et al. [11] also showed lipids forms inclusion complexes with the helical structures of amylose which in result influenced the swelling and viscoelastic properties of the grain starch. It is reported that during the phase of grain development, accumulation of amylose content in rice is significantly affected due to genetics of the crop as well as temperature. In the same way, protein contents are reported to be increased at lower temperatures, which results in a higher content of amylose in ripened grains of rice [12].

It has been reported by many researchers that average rice yield as well as its nutritional and cooking quality are significantly affected by weather conditions. Studies carried out on rice demonstrated the negative impact of drastic changes in rainfall patterns coupled with rising temperatures could be managed by changes in planting dates, transplanting dates, transplant age and crop spacing [13]. Therefore, the present study was aimed at evaluating nutritional, physico-chemical, milling and cooking quality attributes of eight Basmati rice cultivars in response to different transplanting dates.

The experiment was conducted during Kharif season of 2015 at the research farms of Rice Research Institute, Kala Shah Kaku, Pakistan. Average, maximum and minimum values of temperature and precipitation during whole the year 2015 are shown in Figure 1. The experiment was laid out in Randomized Complete Block Design (RCBD) replicated thrice. The treatments included four dates of transplanting (1^st and 23^rd June, 14^th July and 5^th August). Eight advance rice lines and cultivars i.e. Basmati 515, RRI-3, PK9194, PKBB15-1, PKBB15-6, PKPB-8, PK10683 and PS2 (as check) were used in the study.

Figure 1: Temperature goes below 21°C and day length period shortens to 11 h 50 min.

Seedling of 30 days old nursery of each variety was transplanted on a well puddled soil with a spacing of 20 cm between rows and 20 cm between hills. Puddling was done by running a cultivator in standing water (75 mm) followed by planking. Forty kg N ha-1 was applied at 5 DAT. The crop was maintained according to the recommended doses of fertilizers. All the other agronomic practices were carried out according to the recommendations. At harvest, grain yield was measured at 14% grain moisture content. After harvesting paddy samples were stored for one and a half months at room temperature and then milled.

The results of ANOVA indicated the highly significant (p>0.01) variation among the genotypes for Brown Rice percentage (BR%), Total milling recovery (TMR%), Hear rice recovery (HR%), Cooked grain length (CGL) and Bursting percentage (B%). In grain shape quality traits, only average grain length before cooking showed highly significant (p>0.01) variation among the studied genotypes while the other two traits, grain width and thickness showed significant (p>0.05) variation. Likewise, amylose percentage was significantly (p>0.05) different while protein contents showed non-significant variations among the genotypes.

The results also confirmed that most of the almost all the studied genotypes showed flowering initiation after mid-September when the minimum temperature goes below 25°C whereas day length period less than 12 h 17 min; and continue flowering till first half week of October when the temperature goes below 21°C and day length period shortens to 11 h 50 min as depicted in Table 1 and Figure 1.

Table 1: Average, minimum and maximum values of all the traits of all the genotype under different transplanting dates.

Results of brown rice (BR) percentage as indicated by Figure 1a indicates there was no significant difference in average brown rice of all the studied genotypes harvested from first D1 (78%) and second D2 (78%) dates, but it significantly reduced in third date D3 (77%) and remained constant in fourth date D4 (77%). The same comprehension may be drawn out from results of average Total Milling Recovery (TMR) percentages of rice from each date. First two dates D1 and D2 are non-significantly different from each other (68% and 67% respectively), while it reduced significantly in D3 (65%) and the increased non-significantly in fourth date D4 (66%) as depicted in Figure 1a. However, head rice recovery was among the yield and quality trait that was mostly affected by different transplanting dates, variations in temperature, humidity and photoperiodism. The results of this study indicate that the head rice recovery significantly increased with the delay of transplanting dates from D1 to D4 as depicted in Figure 1a. It increased from 34% in D1 to 36% in D2, then to 39% in D3 and they further increased non-significantly to 40% in D4.

Figure 1a: Indicates there was no significant difference in average brown rice.

Figure 1b depicts the results of Cooked Grain Length (CGL) and Bursting (B) percentages of averaged data of all the studied Basmati genotypes transplanted at different dates. The results showed non-significant variation among the average of all the genotypes in different dates D1 to D4 in case of CGL indicating non-significant effect of climatic factors on cooked grain length of the Basmati genotypes. However, bursting percentage was highly affected by the changing climatic factors from D1 to D4. Highest bursting percentage was observed in D1 (5.6%) that gradually decreased to 3 and 2.1% in D2 and D3 respectively, that again increased to 2.8 in D4.

Figure 1b: Depicts the results of cooked grain length (CGL) and bursting (B).

Grain shape quality traits i.e. average grain length, average grain width and average grain thickness is depicted in Figure 1c as observed in all the four transplanting dates. Non-significant variations were observed in cases of average grain width and average grain thickness. Highest AGT was observed in D1 (1.4 mm) and lowest was in D3 (1.2 mm) while the AGT was constant on all the dates i.e. 1.5 mm in all the dates indicating no effects of climatic factors on thickness of grain of Basmati lines. On the other hand, AGL was most affected among all the studied grain shape quality traits as depicted in Figure 1c. The figure showed that maximum AGL was observed in first date D1 (8.4 mm) that decreased to 8.1 mm in D2 and remained constant although with the delay in translating dates in D3 and D4 with the same value of 8.1 mm.

Figure 1c: Non-significant variations.

Figure 1d shows the variation in amylose and protein contents of milled rice grains harvested from different transplanting dates. In case of amylose contents, it gradually increased from 7.78 in first date D1, up to 8.10 mm in third date D3 that decreased non-significantly in fourth date D4. On the other hand, protein contents were more influenced by transplanting at different dates. At first date D1, 23.21% protein contents were recorded that decreased non-significantly in D2. In third date D3, protein content significantly increased to 24.44 mm in date third D3 showing maximum protein contents and then decreased significantly to 8.04 mm in fourth date.

Figure 1d: Shows the variation in amylose and protein contents.

Results depicted in Figure 2a-2d shows the individual performance of each genotype (Table 2). Among all the studied genotypes, Basmati 515 showed maximum average brown rice % (81.3%) of all the four transplanting dates, followed by PK9194 (79.3%), PKBB15-6 (78.9%) and PK10683 (77.5%) while the minimum was observed in PKPB-8 (74.3%). Likewise, maximum TMR was recorded again in Basmati 515 (75%) followed by PK9194 (70.8%) and minimum (62.4 and 62.5%) was observed in both PKBB15-1 and PKPB-8. Maximum (61.3%) head rice recovery HR was observed again in Basmati 515, followed by PK9194 (56.8%) and PKBB15-6 (51.8%) while the rest of the genotypes showed less than 30% HR except PKBB15-1 that showed 32% head rice recovery. Minimum (19.6%) HR was observed in RRI 3 which had the longer average grain length. The results indicated that extra-long grain rice varieties are more vulnerable to breakage during milling processes and hence are lower in head rice recovery, thus proving their suitability for parboiling.

Figure 2a-2d: Shows the individual performance of each genotype.

Table 2: Average values of all the traits against each genotype under different transplanting dates.

In case of cooked grain length (CGL) maximum CGL was observed in PKPB-8 (16.75 mm) followed by RRI-3 (16.6 mm), PS2 (16.53 mm) and PK10683 (16.50 mm) while the minimum CGL was showed by PKBB15-1 (11.35 mm). Rest of the genotypes showed more than 13 mm cooked grain length. Maximum bursting was observed in Basmati 515 (6.25%) that was not too high to affect the overall ranking of the genotype based on its quality traits. All the other genotypes showed less than 3% which is acceptable.

In case of grain shape quality traits, average grain length (AGL) was highest (8.58 mm) from PS2 and PK10683, followed by PKPB-8 (8.51%), RRI-3 (8.37%) and PKBB15-1 (8.26%) while the minimum was recorded in PKBB15-6 (7.50 mm) as depicted in Figure 2c. PS2, RRI- 3, PK10683 and PKPB-8 are bolder grain varieties with AGW of 1.55 mm, 1.53 mm, 1.53 mm and 1.50 mm respectively. On the other hand maximum average grain thickness (AGT) was observed in Basmati-515 (1.31 mm), followed by KPB-8 and PS2 (1.29 mm both) and RRI-3, PK9194, PKBB15-1 and PK10683 (each with 1.28 mm AGT) while the minimum was observed in PKBB15-6 (1.25 mm) as depicted in Figure 2c.

Amylose content is the most important trait in case of Basmati type rice varieties that contributes much in cooking quality of the cooked rice. Average data of amylose and protein contents in milled grains of all the studied rice genotypes showed that maximum (25.19%) of amylose was found in Basmati 515, followed by PK9194 (24.79%) and PKBB15-6 (24.38%) while the minimum was found in PKBB15- 1 (22.31%) as depicted in Figure 2d. Likewise, maximum protein contents were recorded in PKBB15-6 (8.25%), followed by PKBB15-1 (8.16%), PS2 (7.98%), RRI 3 (7.90%) and then PK10683 and PKPB-8 with 7.88% protein contents in their milled rice, while the minimum was present in Basmati 515 (7.78%) as given in Figure 2d.

The results of ANOVA indicated the highly significant (p>0.01) variation among the genotypes for Brown Rice percentage (BR%), Total milling recovery (TMR%), Hear rice recovery (HR%), Cooked grain length (CGL) and Bursting percentage (B%). In grain shape quality traits, only average grain length before cooking showed highly significant (p>0.01) variation among the studied genotypes while the other two traits, grain width and thickness showed significant (p>0.05) variation. Likewise, amylose percentage was significantly (p>0.05) different while protein contents showed non-significant variations among the genotypes. The results suggested that all the pure basmati lines or genotypes initiates flowering within a specific range of day length duration and temperature. Delaying the transplanting date did not affect the flowering time of studied basmati lines that indicates the lines were pure basmati in nature and had a strong basmati background. Maximum average yield was observed between 23^rd June and 14^th of July as depicted by yield data of all the dates. Head rice recovery was increased by delaying the dates of transplanting. Protein and amylose contents were recorded highest when lines were transplanted on 14^th of July. Bursting was reduced with the delayed transplanting while cooked grain length showed no significant changes with delay in transplanting. Average grain length, average grain thickness and width also remained unchanged by transplanting delay. The results also confirmed that most of the almost all the studied genotypes showed flowering initiation after mid-September when the minimum temperature goes below 25°C whereas day length period less than 12 h 17 min; and continue flowering till first half week of October when the temperature goes below 21°C and day length period shortens to 11 h 50 min. The head rice recovery significantly increased with the delay of transplanting dates from D1 to D4 as depicted in Figure 1a. It increased from 34% in D1 to 36% in D2, then to 39% in D3 and they further increased non-significantly to 40% in D4. Average data of amylose and protein contents in milled grains of all the studied rice genotypes showed that maximum (25.19%) of amylose was found in Basmati 515, followed by PK9194 (24.79%) and PKBB15-6 (24.38%) while the minimum was found in PKBB15-1 (22.31%). maximum protein contents were recorded in PKBB15-6 (8.25%), followed by PKBB15-1 (8.16%), PS2 (7.98%), RRI 3 (7.90%) and then PK10683 and PKPB-8 with 7.88% protein contents in their milled rice, while the minimum was present in Basmati 515 (7.78%). Maximum yield was observed in PS2, followed by Basmati515, PKBB15-6, PK10683 and PKPB8 while minimum was observed in PKBB15-1.