Donor plant material and introgression lines development
The backcross introgression lines in hexaploid background were developed earlier. These lines were developed at the Punjab Agricultural University in a two-step process. First the target region for grain zinc concentration was introgressed from diploid (T. monococcum
and T. boeoticum
) to tretraploid (T. durum
) wheat background. Eight T. durum
lines with high zinc concentration (>60 ppm) represented as BF13, BF14, BF18, BF20, BF21, BF22 (BC1F7 developed from T. monococcum
W49-27-1 backcrossed to T. durum
cv Aconchi89) and BF25 (T. boeoticum
49992 backcrossed to T. durum
cv PDW274) were shortlisted. These were used as donor for the introgression of target region for grain zinc concentration into the hexaploid wheat i.e.
HD2967 and WH1105 (high yielding wheat cultivars of the North West Plain Zone of India); PBW698 and PBW703 (gene pyramided versions of PBW343 carrying major rust resistance genes Yr10
). The F1’s were backcrossed two times with high yielding wheat cultivars to sufficiently recover the genetic background of elite cultivars (Singh C., 2016)
. The development of material as well as further breeding work was carried out in the Department of Plant Breeding and Genetics at Punjab Agricultural University, Ludhiana and Off season station Keylong (Himachal Pradesh).
Material studied in present experiment
The material used in the present investigation comprises of eight agronomically superior high zinc BC1F5 lines and ten high zinc BC2F5 derivatives in the background of high yielding wheat varieties and advanced lines. The field experiments were laid out in a randomized block design with three replications in at two locations i.e.
Punjab Agricultural University, Ludhiana (30°54'N and 75°51'E.) and PAU Regional Research Station, Gurdaspur (32°2'N and 75°24') for testing the effect of environment on grain iron and zinc concentration during main season 2016-17. Experimental units consisted of 4 rows of 1.75 m length spaced 20 cm apart. Total entries used in this experiment were thirty including 18 backcross derivatives, 7 donor parents (BF13, BF14, BF18, BF20, BF21, BF22 and BF25), 4 high yielding recipient parents (HD2967, WH1105, PBW698 and PBW703) and one high yielding variety PBW725 as check.
Observations were recorded on days to flowering, plant height, days to maturity, tillers per meter row length, spike length, number of spikelets per spike, grains per spike, thousand grain weight, grain yield per plot (g), grain protein content (%), grain zinc concentration (ppm), grain iron concentration (ppm) and grain yellow pigment content.
Grain protein content (%)
The grain protein content was assessed using the whole grain analyzer “Infratec1241” supplied by M/S Foss Analytical AB, Sweden. It utilizes the near infrared light which is transmitted through the grains. The grain samples were scanned in the range of 850 to 1050 nm with a bandwidth of 7 nm and there were 100 data points per scan. The results were displayed as percent protein content along with per cent moisture.
Grain iron and zinc concentration (ppm)
Energy dispersive X ray fluorescence (EDXRF) method was used to determine iron and zinc concentrations in wheat grains. EDXRF was carried out utilizing an Oxford Instruments X-Supreme 8000 fitted with a 10 place auto-sampler. Estimation conditions were as recommended by the producer for grain zinc and iron analysis in a cellulose matrix.
Yellow pigment content (ppm)
Yellow pigment content in the wheat wholemeal was estimated using a standard AACC colorimetric method. Four gram wholemeal was weighed and put into a 125 ml reagent bottle to which, 20 ml water saturated n-butanol was added. Bottle was shaken properly to mix the contents and kept in dark for 16 hours. The extract was obtained after filteration of the contents into standard test tubes. The intensity of colour of extract was read at 440 nm using Spectronic20+D spectrophotometer and recorded as optical density (O.D.). Yellow pigment content was calculated using the following formula:
Yellow pigment content (ppm) = [(O.D. x 23.5366) + 0.0105]