Induced mutagenesis breeding through acute and chronic gamma irradiation for yield improvement in two Bambara groundnut [Vigna subterranea (L.) Verdc.] varieties

Bambara groundnut [Vigna subterranea (L.) Verdc.] is a highly nutritious underutilized legume with enormous potentials to sustain global food security. However, limitations due to the crop flower's autogamous and small nature had limited its potential for improvement through conventional breeding with a <2% success rate recorded from the previous studies. Thus, the most viable method of improving this crop is by creating genetic variability through induced mutagenesis. This study was conducted to induce genetic variability in two Bambara groundnut varieties (Ex-Sokoto and Karo) through acute and chronic gamma irradiation to developed high-yielding varieties. Healthy seeds were exposed to acute gamma irradiation using Cesium-137 at the doses of 0 (Control), 25, 50, 75, 100, 125, 150, 175, 200, 250, and 300 Gy. For chronic irradiation, two weeks old healthy seedlings were exposed to the accumulated doses of 0 (Control), 8.52 (Ring 2), 17.04 (Ring 3), 35.56 (Ring 4), 34.09 (Ring 5), 42.61 (Ring 6), 59.65 (Ring 7), 93.74 (Ring 8), 144.87 (Ring 9), 255.64 (Ring 11) and 570.94 (Ring 15) Gy respectively for 852:08 hours in Gamma Green House (GGH) at Nuclear Malaysia until physiological maturity. The experiments were laid down in Randomized complete block design (RCBD) with three replications and four treatments for acute gamma irradiation. However, for chronic gamma irradiation, it was (RCBD) with three replications and eleven treatments at field 15 Faculty of Agriculture, Universiti Putra Malaysia. The results for optimum lethal dose (LD) indicated highly significant differences (p ≤ 0.01) for all evaluated traits except for internode length, which did not show any significant difference (p ≤ 0.05). The established lethal doses (LD25%, 50%, 75%) for acute gamma irradiation were 73, 160, 248 Gy and 68, 148, 227 Gy for Ex-Sokoto and Karo varieties. Similarly, for chronic gamma irradiation, the established lethal doses (LD25%, 50%, 75%) were 47, 250, 444 Gy and 70, 264, 452 Gy for Ex-Sokoto and Karo varieties. The frequency of chlorophyll mutants identified includes; albina, chlorina, xantha, viridis, maculata, and virescent. The occurrence of a virescent type of chlorophyll mutants was the highest between the two varieties. In acute, chlorophyll mutants' overall effectiveness and efficiency were 6.43 and 22.06 among EX-Sokoto, while 4.58 and 17.35 were identified among the Karo variety. Similarly, in the chronic phase, chlorophyll mutants' overall effectiveness and efficiency were 12.02 and 11.51 among EX-Sokoto and 12.56 and 12.09 among Karo variety. The most noticeable macro mutants identified in this study were linked to the plant height, flowering and maturity period, pods, leaf, and growth habits. The results from both acute and chronic mutagenesis at M1 to M4 generations display significant improvements among the different mutagens doses used in this study. It was observed that both acute and chronic gamma irradiation stimulates plant growth at low and moderate gamma irradiation doses compared to the higher gamma irradiation doses. Most of these mutants were identified in the acute phase at the range of 68 to 150 Gy and 73 to 160 Gy for Karo and Ex-Sokoto varieties. Therefore 150 Gy and 160 Gy are regarded as appropriate gamma irradiation dose rates that can be used to induce viable mutants in these varieties. Similarly, among the chronic gamma-irradiated mutants, the most outstanding doses include; 42.61 (ring 7), 25.56 (ring 9), 144.87 (ring 4) and 59.56 (ring 6). Significant improvement was achieved in yield and yield components in both acute and chronic gamma irradiation methods. In the acute phase, the highest mean yield recorded was 10.07 (ESK 250-P11) and 11.60 (KRO 70- P16) t ha−1 for EX-Sokoto and Karo varieties. In contrast, 10.37 (ESK R14-P6) and 10.85 (KRO R9-P4) were recorded as the highest mean for EX-Sokoto and Karo variety in the chronic phase. This result is more than two folds of the reported mean yield per hectare in most existing varieties, including the two used in this study. There was high heritability coupled with high genetic advance for most of the studied traits in yield and yield components both in acute and chronic mutagenesis in this study. Therefore, effective selection can be achieved using those traits in subsequent generations. Among acute established mutants, ESK 75-P7 5.11, ESK 75-P15 6.99, ESK 160-P17 7.61, ESK 250-P11 10.07, ESK 250-P7 7.18 and KRO 70-P16 11.60, KRO 70-P5 6.60, KRO 150- P3 11.16, KRO 230-P3 7.68, KRO 230-P3 6.60 were identified as mutants that can be used for further study. For chronic mutants, ESK R6-P9 6.64, ESK R7-P4 6.76, ESK R8- P7 7.47, ESK R11-P5 8.97, ESK R11-P5 6.80, ESK R14-P6 10.37 and KRO R3-P1 6.00, KRO R6-P7 9.44, KRO R7-P3 6.62, KRO R8-P7 7.58, KRO R9-P4 10.85, KRO R11- P9 9.93 can be used. Yield per plant observed a highly significant and positive correlation with most of the rest of the traits studied. In conclusion, this study discovered that induced physical mutagen through acute and chronic gamma radiation effectively induces morphological genetic divergence in Bambara groundnuts and has established the successful approach of induced physical mutagenesis in the two varieties used in this study

Evaluation of radiological risk associated with local building materials commonly used in Northwestern Nigeria

In this study, potential radiological risk due to the activity concentrations of primordial radionuclides (226Ra, 232Th, and 40K) in commonly used local building materials (sand, clay, kaolin and gypsum) in Northwestern Nigeria were assessed using NaI (Tl) detector. The measured activity concentrations ranged from 47 to 63 Bq kg−1 for 226Ra, 24–32 Bq kg−1 for 232Th, and 219–257 Bq kg−1 for 40K respectively. The mean values of 232Th, and 40K for all samples were below the respective world averages of 45 and 420 Bq kg−1 with that of 226Ra for all the samples higher than the world average value of 32 Bq kg−1. The potential radiological risks were assessed by determining radium equivalent activity (Raeq), internal and external hazard indices (Hin and Hex), absorbed gamma dose rates (DR), internal annual effective dose rates (IAED), and annual gonadal dose equivalent (AGDE) and activity utilization index (AUI). The assessed parameters were found to range between 104 and 125 Bq kg−1, 0.99 to 1.15, 0.28 to 0.34, 48 to 58 nGyh−1, 0.76 to 0.86 mSvy−1, and 0.78 to 0.96 respectively. The Raeq and DR for all the analyzed samples were found to be within International recommended limits of 370 Bq kg−1 and 59 nGy h−1 as recommended by UNSCEAR

Drought resistance in rice from conventional to molecular breeding: a review

Drought is the leading threat to agricultural food production, especially in the cultivation of rice, a semi-aquatic plant. Drought tolerance is a complex quantitative trait with a complicated phenotype that affects different developmental stages in plants. The level of susceptibility or tolerance of rice to several drought conditions is coordinated by the action of different drought-responsive genes in relation with other stress components which stimulate signal transduction pathways. Interdisciplinary researchers have broken the complex mechanism of plant tolerance using various methods such as genetic engineering or marker-assisted selection to develop a new cultivar with improved drought resistance. The main objectives of this review were to highlight the current method of developing a durable drought-resistant rice variety through conventional breeding and the use of biotechnological tools and to comprehensively review the available information on drought-resistant genes, QTL analysis, gene transformation and marker-assisted selection. The response, indicators, causes, and adaptation processes to the drought stress were discussed in the review. Overall, this review provides a systemic glimpse of breeding methods from conventional to the latest innovation in molecular development of drought-tolerant rice variety. This information could serve as guidance for researchers and rice breeders

Effects of grafting on morphophysiological and yield characteristic of eggplant (Solanum melongena L.) grafted onto wild relative rootstocks

Grafting is regarded as an integral component of sustainable vegetable production. It is important in the management of soil-borne diseases, and reports suggest that grafting with viable rootstocks can enhance crop growth and yield. This research was conducted using splices and cleft grafting techniques to investigate graft compatibility among varieties of high yielding eggplant scion (MCV1, MCV2, CCV1, CCV2, CCV3, NCV, and TCV) grafted onto wild rootstocks (MWR, BWR, and TWR) to study their morphophysiological and yield characteristics. High yielding scions grafted onto wild relative rootstocks were compared with two controls including self-grafted and non-grafted. All the scion had a high rate of germination (≥95%) and remarkable graft success (100%) was recorded in MCV1, MCV2, and TCV using the cleft techniques. Generally, the use of rootstocks resulted in higher total and marketable fruit yield compared to the non-grafted and self-grafted scion plants, respectively. In particular, MWR and TWR rootstock conferred the highest vigour to the scion, resulting in the highest values recorded for total and marketable fruit yield, number of fruits per plant and average fruit weight. A similar result was obtained in fruit length and diameter, where long and wide fruits were observed in scions grafted onto MWR and TWR rootstocks, respectively. Grafting of high yielding eggplant scion onto resistant MWR, BWR and TWR eggplant rootstock was found to be beneficial for eggplant cultivation. The remarkable compatibility and vigour of the rootstock with scion led to the improvement in total and marketable yield of the fruits. As such, it can be concluded that the use of wild relative rootstocks of eggplant species can be a valuable method of improving eggplant production

Marker-assisted introgression of multiple resistance genes confers broad spectrum resistance against bacterial leaf blight and blast diseases in Putra-1 rice variety

Bacterial leaf blight caused by Xanthomonas oryzae pv oryzae (Xoo) and blast caused by Magnaporthe oryzae are major diseases responsible for significant yield loss in rice production across all rice growing regions. Host plant resistance has been advocated as a sustainable means of guarding against the diseases. This experiment was conducted with the aim to introgress multiple resistance genes against bacterial leaf blight and blast diseases through marker-assisted backcross breeding. Two dominant (Xa4 and Xa21) and two recessive (xa5 and xa13) Xoo resistance genes were introgressed into a high yielding Malaysian rice variety Putra-1 with genetic background of three blast resistance (Piz, Pi2 and Pi9) genes. Eight polymorphic tightly linked functional and SSR markers were used for foreground selection of target genes. Seventy nine polymorphic SSR markers were used in background selection. The plants were challenged at initial stage of breeding and challenged again at BC2F2 with the most virulent Malaysian pathotypes of Xoo (P7.7) and Magnaporthe oryzae (P7.2) to test their resistance. Results obtained from foreground marker segregation analysis at BC1F1 and BC2F1 showed that the marker polymorphism both fitted into the Mendel’s single gene segregation ratio of 1:1 for both Xoo and blast resistance. At BC2F2, results indicated that foreground marker polymorphism fitted into the expected Mendelian ratio of 1:2:1 for blast resistance only. Marker-assisted background selection revealed high percentage of recurrent parent genome recovery (95.9%). It was concluded that the inheritance of blast resistance in the introgressed lines was mainly due to single gene action while the inheritance of Xoo resistance was substantially due to single nuclear gene action. The incorporation of four bacterial leaf blight and three blast resistance genes (Xa4 + xa5 + xa13 + Xa21; Pi9 + Pi2 + Piz) in the newly developed lines would provide for broad spectrum and durable resistance against the two major diseases studied