Regulation of Flowering Time by Improving Leaf Health Markers and Expansion by Salicylic Acid Treatment: A New Approach to Induce Flowering in Malus domestica

In the external coincidence model, internal and external molecular signals, provided by the circadian clock and sunlight, respectively, are required to induce flowering. Salicylic acid (SA) applications during floral induction have multiple effects. In the current study, Malus × domestica plants were exposed to SA during the flower-induction stage to analyze the effect on various health markers and flowering. A total of 56 equal-sized Fuji/M9 trees that were about 7 years old were randomly divided into two groups. The first group (SA-treated) was sprayed with 4 mM SA solution, while the second group was sprayed with distilled water which served as control (CK). The SA applications increased various leaf pigments. Abiotic stress markers were increased in CK during the flower-induction stage. In the SA-treated group, non-enzymatic antioxidants increased, whereas in the control group, enzymatic antioxidants increased during the flower-induction stage. Histo-morphometric properties of leaves were significantly improved in the SA-treated group. The relative expression of the mRNA levels of MdMED80, −81, −3, and −41 were significantly increased in SA-treated leaves, leading to an early and increased flowering phenotype. Thus, SA increased leaf expansion and health-related marker levels, which lead to early induction of flowering in M. domestica. Overall, our work established a role for leaf health assessments in the regulation of flowering in M. domestica.

Rootstock Affects Floral Induction in Citrus Engaging the Expression of the FLOWERING LOCUS T (CiFT)

In Citrus, flower induction represents the transition from vegetative to reproductive growth. The regulation of flower induction is mainly triggered by exposure to low temperatures and water-deficit stress, which activates the signaling cascade leading to an increased expression of the citrus orthologs of the FLOWERING LOCUS T (CiFT). In this study, the relationship between rootstock and flower induction under Mediterranean field conditions was investigated by monitoring the expression levels of the floral promoter CiFT2 in leaves of the pigmented sweet orange “Tarocco Scirè” grafted onto “C35” citrange and “Swingle” citrumelo rootstocks. The latter two are known to confer, respectively, high and low yield efficiency to the scion. In both rootstock/scion combinations, CiFT2 showed a seasonal expression with a peak during the inductive period in January triggered by cold temperature. The “Tarocco Scirè”/”C35” citrange combination showed the highest expression levels for CiFT2; this increased expression was correlated with yield and a higher number of flowers in the following spring, suggesting a significant effect of rootstocks on flower induction mediated by the overexpression of the CiFT2 gene.

Appropriate Duration of Drought Stress for Madura Tangerine Flower Induction

Cekaman kekeringan merupakan salah satu teknik yang dilakukan untuk menginduksi bunga jeruk keprok di luar musim dalam upaya memenuhi ketersediaan buah jeruk keprok sepanjang tahun. Durasi cekaman kekeringan yang tepat penting dipelajari untuk menghindari cekaman berat dan mendapatkan hasil bunga yang optimum. Penelitian ini bertujuan menentukan durasi cekaman kekeringan yang tepat untuk menginduksi bunga jeruk keprok dataran rendah varietas Madura. Penelitian dilaksanakan di Kebun Percobaan PKHT-IPB dengan ketinggian ± 300 mdpl dari bulan April-Mei 2019. Percobaan dirancang dengan RAK (Rancangan Acak Kelompok) dengan satu faktor perlakuan yaitu durasi cekaman kekeringan dengan lima taraf: tanpa cekaman kekeringan sebagai kontrol, durasi cekaman kekeringan satu minggu, durasi cekaman kekeringan dua minggu, durasi cekaman kekeringan tiga minggu dan durasi cekaman kekeringan empat minggu. Hasil penelitian menunjukkan bahwa durasi cekaman kekeringan mempengaruhi keberhasilan induksi bunga jeruk keprok Madura. Durasi cekaman kekeringan selama 2, 3 dan 4 minggu dengan nilai kadar air secara berturut-turut 81.81%, 65.21% dan 55.39% dari kapasitas lapang berhasil menginduksi bunga. Bunga muncul pada 3, 2 dan 1 minggu setelah rewatering dan pengairan rutin secara berturut-turut pada perlakuan durasi cekaman 2, 3 dan 4 minggu. Tiga minggu tanpa irigasi merupakan durasi cekaman kekeringan optimum untuk induksi bunga jeruk keprok Madura.